Process for producing biodegradable molded item and molding dies therefor

ABSTRACT

Using a metal mold ( 20   a ) consisting of a convex mold part ( 21   a ) and a concave mold part ( 22   a ), a molding material ( 14 ) is placed between a pair of coating films ( 12 ), and after clamping, the molding material ( 14 ) and the coating film ( 12 ) are heated and molded to make a biodegradable expanded molded article, and at the same time, the coating film ( 12 ) is softened and pressure-bonded to a surface of the biodegradable expanded molded article. An exhaust hole ( 31   a ) and ( 32   a ) are provided on the convex mold part ( 21   a ) and the concave mold part ( 22   a ), respectively. At the time of heating and molding, gaseous matter existing between the coating film ( 12 ) and a surface of the metal mold ( 20   a ) is discharged out of the metal mold ( 20   a ) through the exhaust holes ( 31   a ) and ( 32   a ). Accordingly, it is possible to provide a method and a mold to manufacture a biodegradable expanded molded article easily and with excellent accuracy of dimension, having enough strength, enough water resistance, very excellent biodegradability and excellent surface smoothness even if the biodegradable molded article has a complicated shape.

TECHNICAL FIELD

The present invention relates to a method for manufacturing an expandedmolded article mainly made of starch and having biodegradability(biodegradable molded article), particularly to a method formanufacturing a biodegradable molded article that can be desirably usedas a disposable expanded molded article that is disposed after the usesuch as a food container, a molding buffer material, GES and a wrappingtray, and to a mold used therefor. In addition, the present inventionrelates to a method for desirably manufacturing a biodegradable moldedarticle with a deep drawing shape including a bowl-shaped or acup-shaped biodegradable molded article using a substantially flatcoating film.

BACKGROUND ART

As a disposal method for a molded article, a biodegradability disposaltechnique using microbe has been developed and is in the spotlight.Especially, in the biodegradability disposal method above, a method toutilize natural high polymers such as starch and protein has drawnattention in terms of its practicality. This is because the variousbiodegradable plastics have a problem that despite having fine qualityalmost comparable to conventional plastics (non-degradable ordegradable-retardant), practically they cannot be decomposed quicklyenough.

For instance, when a molded article made of the biodegradable plastic isthick, it takes a very long time until the molded article is completelydecomposed, so practically it is not possible to produce the moldedarticle having enough volume. Also, when the molded article made of thebiodegradable plastic is used particularly as a disposable foodcontainer, composting the molded article together with food residues isthe least harmful disposal method for the environment. However, actuallyit is difficult to compost them together since the biodegradable plasticabove is decomposed much slower than the food residues. Furthermore, itis also difficult to crush the molded article to hasten thedecomposition of the biodegradable plastic, because normally the moldedarticle cannot be crushed easily when it has a certain thickness andstrength. Thus it is almost impossible to compost the molded articlemade of the biodegradable plastic.

Whereas starch and protein, etc. are positively evaluated as thematerials because of advantages such as:

-   -   with fine biodegradability, decomposition is quite easy even if        the volume is large;    -   the resources can be acquired easily on account of availability        of vegetable starch that is mass-produced by agriculture; and    -   a molded article with adequate thickness and thermal insulation        can be acquired, since the molded article is usually used as an        expanded molded article.

(1) Japanese Laid-Open Patent Application. No. 5-320401/1993 (Tokukaihei5-320401; published on Dec. 3, 1993, (2) Japanese Laid-Open PatentApplication No. 7-224173/1995 (Tokukaihei 7-224173; published on Aug.22, 1995), (3) Japanese Laid-Open Patent Application No. 7-10148/1995(Tokukaihei 7-10148; published on Jan. 13, 1995), (4) Japanese Laid-OpenPatent Application No. 2000-142783 (Tokukai 2000-142783; published onMay 23, 2000), and (5) Japanese Laid-Open Patent Application No.7-97545/1995 (Tokukaihei 7-97545; published on Apr. 11, 1995) disclosebiodegradable disposal technologies using starch, protein, etc.

First, a molded article derived from the technology (1) or (2) has theadvantages that it has better decomposability than a molded articlemainly made of the biodegradable plastic and is also superior to thosederived from paper/pulps in its diversity of the molded shape, sincenatural starch is used as the main ingredient. However, at the same timethe molded article derived from the technology (1) or (2) has thedisadvantages that it can be used only for limited purposes and isrequired to barrier moisture during storage, due to its poor water andmoisture resistance.

Second, a molded article derived from the technology (3) or (4) ismainly made of starch or similar polysaccharide, and to enhance itswater resistance, a natural resin (dammar resin, shellac resin, etc.) iscoated on the surface of the molded article to form a water-resistantcoating film.

However, the surface of the molded article (including an expanded moldedarticle) mainly made of starch cannot be completely smoothed, andgeneration of small irregularities cannot be avoided. Thus smallpinholes are likely to be formed on the surface corresponding to theirregularities on the water-resistant coating film if it is simplycoated. It could be possible to render the molded article waterrepellent but difficult to make the same completely water resistant.Particularly, if the molded article is required to bemoisture-resistant, moisture is likely to be absorbed from the pinholeson the water-resistant coating film, and the molded article tends tobecome disfigured.

Furthermore, the dammar resin or the shellac resin must be dissolved inan organic solvent such as alcohol, etc., when applied to the surface.This causes problems in terms of a manufacturing facility. For instance,when the organic solvent is removed after the coating, large-scaleequipment is required to prevent diffusion of the organic solvent in theair that causes air and environment pollution.

Now, on a surface of a molded article derived from the technology (5)that is made of poorly water-resistant biodegradable material such asstarch, as in the cases of the molded articles derived from thetechnologies (3) and (4), a biodegradable coating agent composed ofaliphatic polyester being dissolved in halogenated hydrocarbon iscoated. In this case, using a dip method (dip coating method) for actualcoating of the surface, an adequately water-resistant coating film canbe formed even on a complicatedly-shaped molded article.

However, in this method, it is required to remove the halogenatedhydrocarbon used to dissolve the coating agent, and as in the cases ofthe technologies (3) and (4), problems such as a requirement ofequipment to prevent diffusion of halogenated hydrocarbon. Manyhalogenated hydrocarbons are often harmful for a human body and theenvironment, and the halogenated hydrocarbon that is specificallymentioned in the technology (5) contains CFC so that it should bereleased to the air as little as possible. On this account, alarge-scale hermetic room and a reclaiming device are required as theequipment above.

In addition to the technologies introduced above, there is a technologyin which wax or hydrophobic protein, prepared as a coating solution, iscoated on the surface of the molded article. Generally speaking, it isdifficult to coat a water-resistant coating film on the surface of themolded article evenly and entirely, while coating on a flat moldedarticle such as a flat plate is relatively easy. However, smallirregularities are likely to be formed on the surface of the moldedarticle mainly made of starch as described above and obstruct theformation of an even film, and furthermore, the molded article or acoating device has to be rotated when the molded article issubstantially circular in cross section, for instance, like a cup or abowl. Therefore the coating becomes more difficult.

Besides, even if the coating agent can be applied evenly and entirely byusing the dip method, the coating agent runs down before it solidifiesand becomes a coating film, and unevenness is likely to show up on thecoating film.

The wax has a problem of poor heat resistance due to its relatively lowmelting point. In the meantime, although the hydrophobic protein hasbetter heat resistance and does not need the organic solvent, the moldedarticle absorbs water and is softened/deformed in the coating processdue to frequent uses of aqueous solvents.

So, a technology that has been proposed to laminate a water-resistantcoating film instead of coating thereof, more specifically, (6) JapaneseLaid-Open Patent Application No. 11-171238/1999 (Tokukaihei 11-171238;published on Jun. 29, 1999), (7) Japanese Laid-Open Patent ApplicationNo. 5-278738/1993 (Tokukaihei 5-278738; published on Oct. 26, 1993), (8)Japanese Laid-Open Patent Application No. 5-294332/1993 (Tokukaihei5-294322; published on Nov. 9, 1993).

A container of the technology (6), made by a pulp molding method insteadof molding starch, is coated by a water-impermeable or non-absorbingprotective layer. This method has the advantage that the conventionalplastic coating method can be applied almost without any change.However, at the same time the method has problems such as:

-   -   the pulp molding slowly biodegrades since it is mainly made of        fiber so that the molded article cannot be disposed together        with remaining foods, etc.; and    -   only limited types of molded articles can be produced because it        is difficult to make the molded article thicker, and also the        molded article is not suitable for a deep drawing.

Meanwhile, to make a biodegradable container, a thin film made ofbiodegradable plastic is coated on a surface of the biodegradablecontainer of the technologies (7) or (8) made of either one of naturalpolysaccharide or protein, or either of the two materials that ischemically modified but still biodegradable.

In this technology, while the biodegradable plastic is provided as thethin water-resistant coating film, the container itself is made ofnatural polysaccharide or protein, etc. with enough thickness. On thisaccount, the container is sufficiently water-resistant as well asbiodegradable. Thus this technology is particularly promising among thedisposal technologies by biodegradability using starch or protein, etc.

However, the technology (7) is an arrangement that the biodegradableplastic thin film simply coats the main body of the biodegradablecontainer, and a concrete arrangement of the biodegradable container ishardly mentioned.

For instance, when the main body of the biodegradable container ismainly made of polysaccharide or protein, strength of the main bodyshould be cared of, but the technology (7) does not explain about thestrength at all, and also does not explain how the biodegradable plasticthin film is actually coated, for instance, by forming it by the coatingmethod or by attaching preformed film, etc.

Moreover, the technology (7) does not stipulate the coating state of thebiodegradable plastic thin film on the main body of the biodegradablecontainer at all. The biodegradable plastic thin film coats the mainbody of the biodegradable container mainly made of polysaccharide orprotein, to improve water resistance of the main body. But thetechnology (7) does not mention how the main body is coated, except thatit is simply coated.

Even if the biodegradable container is used as a disposable one, thecontainer should still have a stability and durability as a one-waycontainer. So the biodegradable plastic thin film should not fall offfrom the main body of the biodegradable container. The coating state onthe main body is an important factor, but no description with respect tothis can be found in (7).

Furthermore, as already described, it is difficult to use biodegradableplastics for a thick molded article due to its slow biodegradability.The speed of the biodegradability also greatly depends on not only thethickness of the molded article but also a total amount of biodegradableplastics contained in the molded article. The technology (7) onlydescribes that effectiveness of the biodegradability is improved if themain body of the biodegradable container is expanded, and there are nocomments on a relationship between a degree of the expansion and thebiodegradability, and a balance between the biodegradability of thebiodegradable plastic and that of the main body of the biodegradablecontainer. As a result, it is not possible to manage thebiodegradability of the whole container favorably.

In the meantime, the technology (8) can be assumed to correspond to oneof the manufacturing technologies of the biodegradable containerdisclosed in the technology (7). In this technology, a thermoplastic isdissolved in a solvent and coated on the surface of the main body of thebiodegradable container. Then after the solvent is dried andvolatilized, another coating thin film made of thermoplastic islaminated and bonded by thermo compression. That is to say, thetechnology (8) discloses that thermoplastic is used as an adhesive tobond the coating thin film (equivalent to the biodegradable plastic thinfilm) securely.

Now, as described in relation to technologies (3) to (5), when thethermoplastic dissolved in the solvent is used, problems than anequipment to prevent diffusion of the solvent is required. Moreover, anembodiment of the technology (8) uses chloroform as the solvent, whichshould be scattered in the air as little as possible. Thus, as in thecase of the technology (5), a large-scale hermetic room and reclaimingdevice are required as the equipment above.

Also, the manufacturing process of the technology (8) acquires the mainbody of the biodegradable container by press-molding a sheet made ofpolysaccharide or protein that is preformed by a metal mold. Thus it isimpossible to mold molded articles such as a container with deep drawingshape like a cup, or molded articles having irregular thickness like afood tray with partitions or a wrapping tray, and molded articles havingcomplicated shape like cushioning materials for wrapping.

Other biodegradable containers or biodegradable molded articles arepublicly known as follows;

(10) Japanese Translations of PCT International Laid-Open PatentApplication No. WO-97/10293 (Tokuhyohei 11-512467; published on Mar. 20,1997), (11) Japanese Translations of PCT International Laid-Open PatentApplication No. WO-94/05492 (Tokuhyohei 8-500547; published on Mar. 17,1994), and (12) Japanese Laid-Open Patent Application No. 6-125718/1994(Tokukaihei 6-125718; published on May 10, 1994).

In addition, a method to fill polyurethane foam using a bag, that is,(13) Japanese Laid-Open Patent Application No. 63-54217/1988 (Tokukaisho63-54217; published on Mar. 8, 1988), has been publicly known.

Also, it has been publicly known that depressure is carried out atvacuum molding of typical foamed plastic;

(14) Japanese Laid-Open Patent Application No. 52-134670/1977(Tokukaisho 52-134670; published on Nov. 11, 1977), (15) JapaneseLaid-Open Patent Application No. 54-127476/1979 (Tokukaisho 54-127476;published on Oct. 3, 1979), (16) Japanese Laid-Open Patent ApplicationNo. 55-73535/1980 (Tokukaisho 55-73535; published on Jun. 3, 1980), and(17) Japanese Laid-Open Patent Application No. 57-1712/1982 (Tokukaisho57-1712; published on Jan. 6, 1982).

The present inventors have applied the invention relating to a methodfor manufacturing a biodegradable molded article including asimultaneous attaching process that a coating film is finally attachedto a surface of the biodegradable molded article by using a slurry ordough molding material mainly made of starch or a derivative thereof andwater added thereto and a coating film mainly made of biodegradableplastic and having at least hydrophobicity, heating the molding materialand the coating film in the mold and molding the biodegradable expandedmolded article into a specified shape through steam expansion, and atthe same time heating, softening and press bonding the coating film(Refer to (9) Application No. WO 02/22353 A1 published on Mar. 21, 2002,PCT International Laid-Open Patent Application No. PCT/JP01/07903 datedSep. 12, 2001, when was not published on the application date that is abasis of the priority claim of the present invention, and thereafter itwas published.)

The above prior invention is an excellent one that can manufacture abiodegradable molded article having excellent biodegradability and waterresistance and reduce manufacturing processes and time.

In the method of Patent (9), the molding material placed between thecoating films is expanded inside a mold through steam expansion andpresses the coating film against the mold. Steam occurring from themolding material is exhausted out of the mold through a canal-formedexhausting part formed at a joint part or a fitting part between moldhalves of the mold from between the coating films. However, if anenclosed space is formed between the coating film and the mold, air ispooled and cannot be escaped. Therefore, pressing of the coating filmagainst the mold stops when pressure by expansion of the moldingmaterial and the pressure of air pooled in the enclosed space isbalanced. Moreover, the coating film is not expanded all over the moldand is not fit to the surface of the mold by air pooled in the enclosedspace. Thus, the biodegradable molded article may not be shaped into thecavity of the mold by the air pooled in the enclosed space. Especially,this appears at a part where at least a certain area of both concavepart and smooth surface continue. In the result, in the biodegradablemolded article to be molded, desirable thickness was not obtained at theconcave part of the mold or slight asperity appeared on a surface of thepart where at least a certain area of smooth surface continues. Thus,the biodegradable molded article has insufficient strength and thebiodegradable molded article having fine appearance and printability wasnot obtained.

In addition, in the invention of the reference (9), in case that thebiodegradable molded article having a deep drawing shape such as abowl-shaped container or a cup-shaped container is manufactured, thecoating film is preformed in the substantially same shape as the outershape of the biodegradable molded article or the coating film wasdivided into film pieces as the development elevation so that the it maybe formed in the substantially same shape as the outer shape of thebiodegradable molded article. Therefore, at least two processes werenecessary to make the biodegradable molded article with deep drawingshape from the coating film.

DISCLOSURE OF THE INVENTION

The present invention takes the problems above into account, and hencethe object is to provide a method and a mold to manufacture abiodegradable molded article having enough strength even withcomplicated shape, enough water resistance, a very excellentbiodegradability, and an excellent surface smoothness, with ease andexcellent accuracy of dimension.

To achieve the purpose above, is a method to manufacture a biodegradablemolded article of the present invention comprises the steps of:preparing: a slurry or dough molding material mainly made of starch or aderivative thereof and obtained by adding water therewith; and a coatingfilm mainly made of a biodegradable plastic and having hydrophobicity;and heating and molding the molding material and the coating film in amold having a given-shaped cavity to mold the molding material throughsteam expansion, and at the same time soften and pressure-bond thecoating film to a surface of a biodegradable expanded molded articleobtained through steam expansion molding, wherein said mold has anexhaust hole; and in the heating and molding step, a gas existingbetween the coating film and a surface of the mold is discharged out ofthe cavity through the exhaust hole.

According to the method above, producing the slurry or dough moldingmaterial mainly made of starch and water mixed therewith, andsteam-expansion molding of this molding material easily allowmanufacture of a highly complicatedly shaped molded article, and makethe molded article have more excellent strength compared with aconventional molded article made of starch, since the resultantbiodegradable expanded molded article includes a certain amount ofwater.

According to the method above, since the coating film is mainly made ofa biodegradable plastic having similar quality to common plastics andhas at least hydrophobicity, it is possible to manufacture thebiodegradable molded article having water resistance. Moreover,according to the method above, the coating film is pressure-bonded to asurface of the biodegradable expanded molded article by heating andmolding in the mold, so it is possible to obtain the biodegradablemolded article of which the coating film is substantially adhered to thesurface and cannot be easily peeled off from the surface. It is thuspossible to more steadily ensure water resistance of the biodegradablemolded article.

In addition, according to the method above, the biodegradable expandedmolded article has a very excellent biodegradability since it is foamwith a large surface area and faster biodegrading reaction.

According to the method above, it is possible to make the biodegradablemolded article in fewer processes and by an easy method, since steamexpansion molding of the molding material and pressure bonding of thecoating film are performed simultaneously.

Moreover, according to the method above, by providing an exhaust hole inthe mold and discharging gaseous matter between the coating film and thesurface of the mold out of the cavity through the exhaust hole at thetime of heating and molding, adhesiveness of the coating film to thesurface of the mold is improve. It is thus possible to obtain thebiodegradable molded article with an excellent surface smoothness,thereby obtaining fine glossy surface and beautiful appearance. Also,such smooth surface makes beautiful printing with no color dulling orshear when printing is performed on the surface of the biodegradablemolded article. In addition, improved adhesiveness of the coating filmto the surface of the mold can make the biodegradable molded articlehaving almost the same size as the design (almost the same size as thecavity of the mold) and realize an excellent accuracy of dimension.

In the method above, a space leading to the cavity through the exhausthole may be formed inside the mold, in the heating and molding step, thespace may be hermetically separated (isolated) from the outside of themold. This can avoid deformation or tear of the coating film due to arapid increase of inner pressure in the cavity in case of rapid moldingor in case of using the coating film with low strength.

In the method above, the gas existing between the coating film and thesurface of the mold may be discharged out of the mold through theexhaust hole in the heating and molding step. This can sufficientlydischarge the gaseous matter existing between the coating film and thesurface of the mold out of the cavity. In result, excellent accuracy ofdimension is realized.

In the method above, the method to supply the molding material in themold may be any one of the following methods;

-   -   (1) a method to place the molding material with the coating film        in the mold    -   (2) a method to pour the molding material on the coating film        before heating and molding after placing the coating film in the        molded article    -   (3) a method to pour the molding material on the coating film        after the coating film starts to be heated and molded in the        mold.        Method (1) is the most convenient of these methods since the raw        materials can be poured at one time.

To achieve the above purpose, the mold of the present invention is amold to heat and mold a slurry or dough molding material mainly made ofstarch or a derivative thereof and obtained by adding water theretothrough steam expansion, said mold being characterized in that said moldis made up of a plurality of mold parts that can fit together and forman internal given-shaped cavity, and each of said mold parts has anexhaust hole there through to discharge a gas in the cavity outsidepiercing through.

According to the arrangement above, since the exhaust hole is providedin each mold part, it is possible to discharge gaseous matter in thecavity to the outside through the above exhaust hole at the time ofheating the molding, when the biodegradable expanded molded article ismolded through steam expansion by heating the molding material insidethe mold. This improves adhesiveness of the molded article to thesurface of the mold, and the biodegradable molded article with excellentsurface smoothness can be obtained. Therefore, it is possible to obtainthe biodegradable molded article with fine glossy surface and goodappearance. Also, such smooth surface makes fine printing with no colordulling and shear when printing is performed on the surface of thebiodegradable molded article. In addition, improved adhesiveness of thecoating film and the surface to the mold can make the biodegradablemolded article having almost same size as the design (almost the samesize as the cavity of the mold) and can realize an excellent accuracy ofdimension.

According to the arrangement above, since the exhaust hole pierces ineach of the mold parts, surface smoothness and accuracy of dimension ofa flat area in the biodegradable molded article is improved, comparedwith the case that the exhaust hole is formed only at the joint part ofthe mold parts.

In addition, if an exhaust groove (groove-shaped exhaust) is provided ona side forming the cavity of the mold parts, the exhaust groove appearsin relief on the surface of the biodegradable molded article. However,in the arrangement above, the exhaust hole pierces in each of the moldparts is used, the exhaust hole does not have any influence on the shapeof the surface of the biodegradable molded article at all or if anyslight but no practical influence.

It is preferable that for the mold of the present invention, the moldparts are made of a metal and an insulator is placed between the moldparts to insulate the mold parts from each other.

According the arrangement above, it is possible to heat the moldingmaterial through high-frequency dielectric heating or electroconductiveheating using each of the mold parts as an electrode. Therefore, it ispossible to uniformly heat the molding material in a short time and toobtain an excellent molded article in a short time. Also, according tothe arrangement above, in case that the biodegradable molded article ismanufactured by the above method, the coating film having the comparablylow melting point can be used, since the coating film is not directlyheated in the mold.

Another purpose of the present invention is to provide a method tomanufacture a biodegradable molded article having a deep drawing shapesuch as a bowl-shaped container or a cup-shaped container with fewerprocesses.

The method to manufacture the biodegradable molded article in accordancewith the present invention has a basic constituent that “comprising thesteps of: preparing: a slurry or dough molding material mainly made ofstarch or a derivative thereof and obtained by adding water thereto; anda coating film mainly made of a biodegradable plastic and havinghydrophobicity; and heating and molding the molding material and thecoating film in a mold having a specific cavity to mold the moldingmaterial through steam expansion, and at the same time soften andpressure-bond the coating film to a surface of a biodegradable expandedmolded article obtained through steam expansion molding”, and ischaracterized in that “inside said mold of a deep drawing shape themolding material and the coating film is placed substantially flat forheating and molding to manufacture a biodegradable molded article of adeep drawing shape” to achieve the above purpose.

The above method has the above basic constituent and the same merit asthat of the method using the mold equipped with the exhaust hole.

Namely, according to the method above, it is possible to easily mold avery complicatedly-shapes biodegradable molded article by preparing theslurry or dough molding material mainly made of starch and water mixedtherewith and molding the molding material through steam expansion, andthe resultant biodegradable molded article has a certain moisturecontent and more excellent strength compared with a conventional moldedarticle made of starch.

Also, according to the above method, since the coating film is mainlymade of a biodegradable plastic having a nature similar to a commonplastic and has at least hydrophobicity, it is possible to manufacture awater-resistant biodegradable molded article.

Also, according to the method above, it becomes possible to manufacturethe biodegradable molded article with fewer processes and easy method,since molding of the molding material through steam expanding andpressure-bonding of the coating film are simultaneously performed.

Additionally, according to the method above, since the coating film ispressure-bonded on the surface of the biodegradable molded article byheating and molding in the mold, the biodegradable molded article ofwhich the coating film is substantially adhered to the surface can beobtained and the coating film hardly peels off from the surface of thebiodegradable molded article. It is thus possible to more certainlysecure water resistance of the biodegradable molded article.

Therefore, the above basic constituents make it possible to easilymanufacture the biodegradable molded article having enough strength,enough water resistance and very excellent biodegradability even with avery complicated shape.

Moreover, according to the method above, since the coating film isplaced substantially flat when pressure-bonding the coating film, asubstantially flat or rolled film on the market can be used as is.Accordingly, a process to preliminarily mold the coating film can beomitted and the manufacturing process can be significantly simplified.

According to the method above, the coating film is placed substantiallyflat, so it becomes possible to supply the coating film easily andcontinuously by transporting with a roller or a clamp. Therefore, thebiodegradable molded article of a deep drawing shape can be continuouslyproduced.

In the specifications of the present invention, “a molded article of adeep drawing shape” has a concave shape having not less than 30 mm indepth and indicates a container that satisfies at least either one of;(1) that a gradient of a side against the center line (a line connectingthe center of a bottom and the center of an opening) is not more that30° at one point, or (2) that a horizontal to vertical ratio (verticalsize/horizontal size) is not less than 0.3. A vertical size means amaximum outer dimension heightwise (along the center line) and ahorizontal size means a maximum outer dimension in a directionperpendicular to the heightwise direction (along the diameter). Means amaximum outside dimension in a direction perpendicular to the verticaldirection.

For a food container, a deep drawing shape usually corresponds to ashape named “glass”, “cup”, “bowl”, “DONBURI”, “WAN”, while a concavecontainer except for a deep drawing shape (hereinafter referred to as ashallow shape) corresponds to a shape called “tray”, “flat plate”,“round plate”, and “square plate”.

In the method above, the coating film is molded directly into a deepdrawing shape by heating and pressure-bonding a substantially flatcoating film in the mold without preliminary molding. Accordingly, thecoating film should be largely drawn at the time of pressure bonding,compared with the case of molding the substantially flat coating filminto a shallow shape such as a plate without preliminary molding or thecase of molding the coating film into a deep drawing shape afterpreliminary molding. However, some varieties of biodegradable plasticscannot be largely drawn at the time of molding, in case that a biaxiallystretched film with excellent heat resistance and gas impermeability isused as the coating film. Therefore, unless the heating conditions ofthe mold are optimized so that the coating film is fully drawn, theremay be some defects such as a tear, a crack or a pinhole on the coatingfilm.

Still another purpose of the present invention is to provide a method tomanufacture a biodegradable molded article that can more steadilyprevent some defects on the coating film and ensure water resistancemore securely, especially in case that the biodegradable molded articleespecially of a deep drawing shape is manufactured using thesubstantially flat coating film.

Another method to manufacture a biodegradable molded article inaccordance with the present invention has the above basic constituents,and to achieve the above purpose, is characterized in that a mold ismade up of a pair of a convex mold and a concave mold being used, themolding material and the coating film is placed between the convex moldand the concave mold before the heating and molding, in the heating andmolding step, a central part of the coating film is deformed by movingat least either one of the convex mold and the concave mold in adirection wherein these two molds fit together, and at least while thecoating film is being deformed, a relative moving speed of the convexmold to a plane formed by connecting a surface of non-deforming parts onan outer periphery of the coating film is maintained from 8 mm/s to 12mm/s.

According to the method above, speed of drawing the coating film by theconvex mold is kept almost consistent and at the optimum speed. So,especially in case that the biodegradable molded article of a deepdrawing shape is manufactured using the substantially flat coating film,it is possible to avoid a tear, crack and a pinhole on the coating film.Since the biodegradable molded article is coated by the coating filmmore securely, it is possible to more steadily ensure water resistanceof the biodegradable molded article.

In the method above, it is preferable that the convex mold and theconcave mold are straightly moved closer to each other at least whilethe coating film is deformed.

According to the method above, for example, compared with the case thatone side of the convex mold and one side of the concave mold areconnected by a hinge to turn the convex mold, pressure applied to thecoating film by the convex mold becomes more uniform. Therefore,especially if a biodegradable molded article of a very deep drawing ismanufactured or if more complicatedly-shaped biodegradable moldedarticle is manufactured, the coating film can be drawn evenly andthickness of the coating film becomes uniform. Accordingly, effect bythe coating film, that is, improvement of water resistance ofbiodegradable molded article is further enhanced.

Also, in the method above, it is preferable to move both convex mold andconcave mold to approximate each other at least until the coating filmstarts to deform.

According to the method above, since both convex mold and concave moldare moved to approximate each other at least until the coating filmstarts to deform, it is possible to reduce time necessary to fit theconvex mold in the concave mold (fitting time), thereby shorteningmanufacturing time.

Also, another method to manufacture a biodegradable molded article inaccordance with the present invention has the above basic constituentsand to achieve still another purpose of the present invention, it ischaracterized in that said heating is done so that the mold has atemperature not less than a softening point of the coating film and atleast 10° C. lower than a melting point thereof.

According to the method above, by making temperature of the mold atleast 10° C. lower than the melting point of the coating film, thecoating film is softened without melting and molded into the shapecorresponding to the mold. It is thus possible to avoid a pinhole on thecoating film especially in case that the biodegradable molded article ofa deep drawing shape is manufactured using the substantially flatcoating film. Accordingly, the biodegradable expanded molded article iscoated by the coating film more securely, which can further ensure waterresistance of the biodegradable molded article.

In the method above, it is preferable that the heating is done so thatthe mold has a temperature not less than 130° C.

According to the method above, since the molding material can be fullyheated and molded through steam expansion, it is possible to reducesteam expansion molding time, to improve the conditions of steamexpansion, and to obtain the biodegradable expanded molded articlehaving even and dense structure. Consequently, it is possible to reducethe manufacturing time and to improve characteristics of the resultantbiodegradable molded article, including strength.

In the method above, it is more preferable that the heating is done sothat the mold has a temperature not less than 150° C.

According to the method above, since the molding material can be morefully heated and molded through steam expansion, it is possible tofurther reduce the steam expansion molding time, to further improve theconditions of steam expansion and to obtain the biodegradable expandedmolded article having more even and dense structure. Consequently, it ispossible to further reduce the manufacturing time and to further improvecharacteristics of the resultant biodegradable molded article, includingstrength.

In addition, in each of the methods above, it is preferable that beforethe above heating and molding, a slip agent (lubricant) is applied onthe surface of the mold contacting the coating film.

According to the method above, contact friction can be reduced betweenthe surface of the coating film and the surface of the mold, therebyavoiding damages including a tear or a crack on the coating film due tofriction with the mold when the coating film is drawn by the mold.

In the specifications of the present invention, the “slip agent” meansan agent used to reduce contact friction between the surface of thecoating film and the surface of the mold after molding and preventadhesion to the mold so that the resultant biodegradable molded articlemay be easily removed from the mold, and it is not limited to what itcalls “a lubricant”.

It is preferable that the above slip agent is a fluoroplastic layerformed on the surface of the mold.

The above method has advantages described below, compared with the casethat liquid slip agent is applied on the surface of the mold contactingthe coating film or the case that a levigated slip agent (inorganicparticles etc.) is adhered to the surface of the mold contacting thecoating film.

Namely, if the liquid slip agent is applied or if the levigated slipagent is adhered, the slip agent comes off the surface of the mold atthe time of molding and should be applied every molding. On the otherhand, in the above method, since the fluoroplastic layer is formed onthe surface of the mold as the slip agent, the slip agent does not comeoff the surface of the mold and can be used for a long time.Accordingly, it is possible to reduce labor to apply the slip agent onthe surface of the mold.

In case that a liquid agent is applied or a levigated slip agent isadhered, the slip agent is adhered on the surface of the biodegradablemolded article at the time of molding, so the slip agent should beremoved from the surface of the biodegradable molded article aftermolding. On the other hand, in the above method, since the slip agent isnot adhered on the surface of the biodegradable molded article duringmolding and does not stain it, labor to remove the slip agent from thesurface of the biodegradable molded article after molding can be saved.

Other and further objects, features and advantages of the presentinvention will appear more fully from the following description. Also,the merits of the present invention will be apparent from the followingdescription taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view describing a method to manufacture abiodegradable molded article in accordance with an embodiment of thepresent invention.

FIG. 2 is a schematic cross-sectional view showing a shape of abowl-shaped container as an example of a biodegradable molded articlemanufactured by a method of the present invention.

FIG. 3 is a schematic cross-sectional view showing a round plate-shapedcontainer as another example of a biodegradable molded articlemanufactured by a method of the present invention.

FIG. 4 is a schematic cross-sectional view and a schematic plan viewshowing a shape of a cup-shaped container as still another example of abiodegradable molded article manufactured by a method of the presentinvention.

FIG. 5 (a) and FIG. 5 (b) are schematic cross-sectional views showing anexample of a structure of a mold to mold the bowl-shaped container shownin FIG. 2.

FIG. 6 (a) and FIG. 6 (b) are schematic cross-sectional views showing astructure of a mold to mold the round plate-shaped container shown inFIG. 3.

FIG. 7 is an explanatory view describing a method to manufacture abiodegradable molded article in accordance with another embodiment ofthe present invention, in order to manufacture the round plate-shapedcontainer shown in FIG. 3.

FIG. 8 is a schematic cross-sectional view showing a structure having anelectrode for internal heating in the mold shown in FIGS. 5 (a) and 5(b).

FIG. 9 (a) and FIG. 9 (b) are schematic cross-sectional views showing anexample of the mold to mold the cup-shaped container shown in FIG. 4.

FIG. 10 (a) and FIG. 10 (b) are schematic cross-sectional views showinganother example of a structure of the mold to mold the cup-shapedcontainer shown in FIG. 4.

FIG. 11 is an explanatory view describing a method to manufacture abiodegradable molded article in accordance with still another embodimentof the present invention, in order to manufacture the bowl-shapedcontainer shown in FIG. 2.

FIG. 12 is an explanatory view describing a method to manufacture abiodegradable molded article in accordance with still another embodimentof the present invention, in order to manufacture the round plate-shapedcontainer shown in FIG. 3.

FIG. 13 is an explanatory view describing a method to manufacture abiodegradable molded article in accordance with still another embodimentof the present invention, in order to manufacture the bowl-shapedcontainer shown in FIG. 2.

FIG. 14 (a) and FIG. 14 (b) are schematic plan view showing an exampleof a coating film cut into two as a film piece when manufacturing thebiodegradable molded article shown in FIG. 4 using a method described inFIG. 15. FIG. 14 (b) is a schematic plan view showing an example of acoating film cut into three as a film part.

FIG. 15 is an explanatory view describing a method to manufacture abiodegradable molded article in accordance with still another embodimentof the present invention in order to manufacture the cup-shapedcontainer shown in FIG. 4.

FIG. 16 is an explanatory view describing a method to manufacture abiodegradable molded article in accordance with still another embodimentof the present invention, in order to manufacture the cup-shapedcontainer shown in FIG. 4.

FIG. 17 is an explanatory view describing a method to manufacture abiodegradable molded article in accordance with still another embodimentof the present invention, in order to manufacture the cup-shapedcontainer shown in FIG. 4.

FIG. 18 is a schematic cross-sectional view showing another structure ofthe mold to mold the bowl-shaped container shown in FIG. 2.

FIG. 19 is a graph showing temporal change in inner pressure of a cavityin the mold with time.

FIG. 20 is an explanatory view describing a method to manufacture abiodegradable molded article in accordance with an embodiment of thepresent invention.

FIG. 21 is a schematic cross-sectional view showing a bowl-shapedcontainer as an example of a biodegradable molded article manufacturedby a method of the present invention.

FIG. 22 (a) and FIG. 22 (b) are schematic cross-sectional views showinga structure of the mold to mold the bowl-shaped container shown in FIG.21.

FIG. 23 (a) and FIG. 23 (b) are schematic cross-sectional views showinghow the coating film deforms in the mold shown in FIG. 22 (a) and FIG.22 (b). FIG. 23 (a) shows when the coating film starts to deform andFIG. 23 (b) shows the course of deforming the coating film.

FIG. 24 is a schematic explanatory view showing an example having anelectrode for internal heating in the mold shown in FIG. 22 (a) and FIG.22 (b).

BEST MODES FOR CARRYING OUT THE INVENTION Embodiment 1

An embodiment of the present invention is described below in accordancewith FIGS. 1 to 18. By the way, the present invention is not limited tothis embodiment.

First, a biodegradable molded article manufactured by a method of thepresent invention is described.

The biodegradable molded article manufacture by a method of the presentinvention contains a biodegradable expanded molded article of a specificshape obtained by molding a molding material through steam expansion,and a coating film attached to a surface thereof, said coating filmbeing mainly made of a biodegradable plastic and having at leasthydrophobicity.

In the above biodegradable molded article, it is preferable that a ratioof volume of air phase included in the biodegradable expanded moldedarticle is more than 30 volume % of total volume of the biodegradablemolded article. This increases a surface area of the biodegradableexpanded molded article and helps to bring in microorganismsbiodegrading the biodegradable expanded molded article. Thus, thebiodegradable expanded molded article is easily biodegraded, therebyfurther improving biodegradability of the biodegradable molded article.

In the description below, the biodegradable expanded molded article issometimes abbreviated to “expanded molded article”. “Slurry” means acondition having sufficient fluidity at least with water added tostarch. Accordingly, starch is not necessarily dissolved in water andmay be close to a suspended condition. In the meantime, “Dough” meansless fluidity than the slurry and may be close to a semi-solidcondition.

An example of the biodegradable molded article is a container shapedinto a bowl (hereinafter, referred to as a bowl-shaped container) thatis a biodegradable molded article of a deep drawing shape. As shown inFIG. 2, the bowl-shaped container 10 a has a main body 11 a of thebiodegradable expanded molded article, and the coating film 12 directlyand substantially attached to the main body 11 a to coat the surfacethereof.

The bowl-shaped 10 a has a side wall 10 aa of upwardly enlargingtruncated cone shape, a bottom 10 ab formed at a lower end of the sidewall 10 aa, and an outwardly extending ring-shaped flange 10 ac providedat an upper end of the side wall 10 aa. On the bottom 10 ab, a foot 10ad, that is, a convex part of the ring shape is formed, so a concavepart 10 ae and a concave part 10 af are formed at the inside and outsideof the foot 10 aa on the bottom 10 ab, respectively.

Another example of the biodegradable molded article is a container of around plate shape (hereinafter referred to as the round plate-shapedcontainer). As shown in FIG. 3, the round plate-shaped container 10 balso consists of the main body 11 b and the coating film 12.

The round plate-shaped container 10 b has a plate-shaped bottom 10 ba, acurved part 10 bb extended from the bottom 10 ba and smoothly curvedupwardly, and an outwardly extending ring-shaped flange 10 bc providedat an upper end of the curved part 10 bb.

Still another example of the biodegradable molded article is a containerof a cup shape (cup-shaped container) which is a biodegradable moldedarticle of a deep drawing shape. As shown in FIG. 4, the cup-shapedcontainer 10 c also consists of the main body 11 c of the biodegradableexpanded molded article and the coating film 12. In FIG. 4, the upperdrawing is a longitudinal sectional view of the cup-shaped container 10c. The lower drawing is a plan view (a drawing looking down thecup-shaped container 10 c) corresponding to the upper drawing.

As described below, the entire surface of the main body 11 a is notnecessarily coated with the coating film 12. It may be coated partly.

A method to manufacture a biodegradable molded article in accordancewith the present invention is a method to use a slurry or dough moldingmaterial mainly made of starch and a derivative thereof and obtained bymixing water therewith, and a coating film 12 mainly made of abiodegradable plastic and having hydrophobicity, to mold through steamexpansion by heating and molding the molding material and the coatingfilm in the mold, and at the same time, to soften and pressure-bond thecoating film on a surface of the expanded molded article obtainedthrough steam expansion molding.

A method to manufacture the biodegradable molded article in accordancewith the present invention is a method to attach the coating film 12directly to the expanded molded article simultaneously with the steamexpansion molding of the molding material. This method has the followingmerits compared with a method to attach the coating film using anadhesive after pre-molding the molding material into the expanded moldedarticle of a specific shape through steam expansion (hereinafterreferred to as after attaching method).

The first merit is to reduce the number of manufacturing processes.Namely, this method can attach the coating film 12 in one process at aminimum and can reduce the number of processes compared with the aboveafter attaching method requiring at least two processes. Also, since itis possible to attach by one process, it can shorten time necessary forproduction, thereby enhancing production efficiency of the biodegradablemolded article in accordance with the present invention.

The second merit is that it not necessary to use an attaching mold.Namely, the coating film 12 is attached at the same time when theexpanded molded article (main body 11 a) is molded by a mold (metal mold20 a). Therefore, it is possible to reduce the cost and space ofmanufacturing equipment since there is no need of attaching equipmentincluding the above attaching mold.

The third merit is that it is not necessary to use an adhesive.Accordingly, it is possible to hold down raw material cost of theadhesive and at the same time to enhance the content ratio of starchincluded in the biodegradable molded article obtained without using theadhesive.

The fourth merit is that in this method, the coating film 12 is formeddirectly on a surface of the expanded molded article (main bodies 11 aand 11 b) and is substantially and cohesively attached to the expandedbiodegradable molded article substantially cohesively, which leads tosteady attaching condition of the coating film 12.

In the method of the present invention, the coating film is attached ata temperature between the softening point (temperature when softeningstarts) of a biodegradable plastic that is a main ingredient of thecoating film and less than the melting point thereof simultaneously withsteam expansion molding of the molding material. Accordingly, thecoating film 12 faces the expanded molded article during expansionmolding process in heated and pressurized condition. In softeningcondition, the coating film 12 is pressurized from the outside by themold, and from the inside by the expanded molded article duringexpanding and molding process. In result, the coating film 12 is fusedand adhered to a surface of the expanded molded article.

In a section of the resultant biodegradable molded article, a boundarysurface between a layer of the coating film 12 and a surface of theexpanded molded article 11 is not smooth as the case of the simpleattaching method (after attaching method). For example, the boundarysurface becomes uneven and irregular surface, and the coating filmbecomes sufficiently adhered to the expanded molded article 11. Inresult, attaching condition of the coating film 12 becomes very strong,and the steadiness is the same as the case with an adhesive layer.Accordingly, it is possible to further improve water resistance and gasimpermeability of the resultant biodegradable molded article.

In addition, the boundary surface between the layer of the coating film12 and the surface of the expanded molded article 11 may have variousshapes depending on components of the coating film 12 and the expandedmolded article 11, or manufacturing conditions.

Generalizing the four merits, the manufacturing method of the presentinvention can manufacture the biodegradable molded article moreefficiently and at lower cost than the after attaching method, therebyoffering the biodegradable molded article at lower price. Consequently,it is possible to more easily use the biodegradable molded article inaccordance with the present invention for disposal purpose.

Next, the molding material used in the present invention is described.The molding material used for the present invention is mainly made ofstarch or a derivative thereof and obtained by mixing water therewith.

Starch used as the main material of the molding material is not limitedto any particular type. For instance, starch easily acquired fromagricultural products worldwide as major cereals, such as potato, corn,tapioca, rice, wheat, sweet potato, etc. can be preferably used. Thestarch above may be either produced from a particular agriculturalproduct or a mixture of starch produced from more than one agriculturalproduct.

Also, a derivative of the starch is a derivative that chemicallymodified but still biodegradable, more specifically, such as α-starch,cross linked starch, and denatured starch. Moreover, a mixture ofunmodified starch and a derivative of the starch can be used. Thus in abroad sense, the starch in the present invention includes unmodifiedstarch (starch in a narrow sense), a derivative thereof, and a mixtureof these two. So, in the description below, “starch” indicates thestarch in a broad sense, unless particularly noticed.

It is preferable that a percentage of starch content is between 50weight % and 100 weight % if a total amount of the main solid matter ofthe molding material is taken as 100 weight %. In addition, it ispreferable that a percentage of starch content is between 20 weight %and 70 weight % if the total molding material containing added water istaken as 100% When the starch content falls in the ranges above, themain material of the biodegradable molded article in accordance with thepresent invention can be regarded as starch, so good biodegradabilitycan be expected. By the way, in the specification of the presentinvention, starch as the main ingredient and an extending agent as anextending additive among various additives are collectively referred toas “main solid matter”.

Apart from the above starch the molding material may include variousadditives. More specifically, the additives are such as extending agent,strength adjusting agent, plasticizer, emulsifier, stabilizer,homogeneity adjusting agent, moisture retaining agent, handlingadjusting agent, conductivity adjusting agent, dielectric loss adjustingagent, swelling agent, coloring agent, etc.

Some additives are beneficial in the manufacturing process, such asimproving production efficiency of the biodegradable molded article oravoiding problems in the manufacturing process, and others areadvantageous for the biodegradable molded article as a finished product,such as improving quality of the resultant biodegradable molded articleand cutting costs thereof. The type of these additives is not limited,unless significantly lowering quality of the expanded molded article orthe biodegradable molded article.

The extending agent is an additive added to the molding material toincrease the bulk of the molding material and decrease the amount ofstarch as the main ingredient as much as possible, to cut costs.Therefore, a substance used as the extending agent is not limited to anyparticular one as long as cheaper than starch, but by-products ofprocessing and manufacturing of foods, etc. are preferably used, todispose the wastes simultaneously.

More specifically, what can be used are:

-   -   (1) a remained juice, residue of squeezing, that are produced in        food (food and drink) processing and manufacturing using        vegetables and fruits such as celery, carrot, tomato, citrus        fruits (mandarin orange, lemon, grapefruit, etc.), apple, grape,        berries, pineapple, sugarcane, sugar beet, etc., and any mixture        thereof;    -   (2) by-products of a manufacturing processed foods using        cereals, such as bean curd lees and tofu;    -   (3) sake lees, shouchu lees, beer yeast lees, wine yeast lees,        etc. that are produced in processes of producing liquors such as        sake, shochu, beer, wine, etc., and any mixture thereof;    -   (4) residues of used luxury drinks such as coffee, black tea,        barley tea, green tea, oolong tea, etc., tea dregs and any        mixture thereof;    -   (5) oil cakes remained after squeezing oil from soybean, corn,        rapeseed, sesame, etc., and any mixture thereof;    -   (6) residues produced in a process to polish cereals such as        wheat bran, rice bran, rice husks, etc., and any mixture        thereof;    -   (7) by-products produced in a process to produce starch such as        gluten meal, etc.;    -   (8) baking residues produced in a process of manufacturing        sweets and bread such as a cone cup, biscuit, wafer, waffle, and        any mixture thereof;    -   (9) the aforementioned by-products etc. being dried or crushed.    -   Either one of the substances or any mixture thereof may be used.

The strength adjusting agent is an additive to adjust (especiallyenhance) strength of the expanded molded article and the biodegradablemolded article. Although the type of the agent is not limited to anyparticular substance, what are taken as the concrete examples are, forinstance:

-   -   the aforementioned by-products (1) to (9) taken as the extending        agents;    -   (10) saccharide such as glucose, dextrin, isomerized saccharide,        etc., and any mixture thereof;    -   (11) sugar-alcohols such as sorbitol, mannitol, lactitol, etc.,        and any mixture thereof;    -   (12) fats and oils such as vegetable fat and oil, animal fat and        oil, processed fat and oil made thereof, etc., and any mixture        thereof;    -   (13) waxes such as carnauba wax, candelilla wax, bees wax,        paraffin, microcrystalline wax, and any mixture thereof;    -   (14) thickener polysaccharide (microbe producing polysaccharide        or vegetable polysaccharide, etc.) such as xanthan gum, gellan        gum, guar gum, locust bean gum, pectin, gum Arabic, karaya gum,        tara gum, carrageenan, furcellaran, agar, alginate, and salts        thereof, and any mixture thereof;    -   (15) chlorides of metals, such as calcium, sodium, potassium,        aluminum, magnesium, and iron; sulfates, organic acid salts,        carbonates, hydroxides, phosphates, and other salts of these        metals; and any mixture thereof;    -   (16) insoluble minerals such as quartz powder, diatomaceous        earth, talc, silicone, etc., and any mixture thereof;    -   (17) vegetable fibers and their derivatives such as cellulose,        microcrystalline cellulose, paper, pulp (used pulp, virgin        pulp), carboxymethyl cellulose, methyl cellulose, acetyl        cellulose, etc., and any mixture thereof.    -   (18) structures of inorganic substances such as glass, metal,        carbon, ceramic, fibers thereof, etc.    -   (19) natural materials such as a shell, bone powder, eggshell,        leaf, wood powder, etc., and any mixture thereof;    -   (20) calcium carbonate, carbon, talc, titanium dioxide, silica        gel, aluminum oxide, non-fiber filler, etc., and any mixture        thereof;    -   (21) fatty acid (stearic acid, lactic acid, lauric acid, etc.),        or salts such as metal salts thereof, etc., fatty acid        derivatives such as acid amide, ether, etc., and any mixture        thereof;    -   (22) other food additives such as glycerin, polyglycerin,        propylene glycol, ethylene glycol, glycerin fatty acid ester,        polyglycerin fatty acid ester, propylene glycol fatty acid        ester, sugar ester, lecithin, sorbitan fatty acid ester,        polysorbate, etc., and any mixture thereof;    -   (23) natural resins such as shellac, rosin, sandarac resin,        gutta-percha, dammar resin, etc., and any mixture thereof;    -   (24) biodegradable resins such as polyvinyl alcohol and        polylactic acid, etc., and any mixture thereof;    -   (25) acetyltributyl citrate, solution of zirconium salt, alkali        solution of ammonium zirconium carbonate, and any mixture        thereof. Either one of the substances above or any mixture        thereof may be used.

The plasticizer is an additive to improve fluidity of the moldingmaterial and gives flexibility to the resultant expanded molded articleand the biodegradable molded article. Although the type of theplasticizer is not limited to any particular substance, what are takenas the concrete examples are, for instance:

-   -   the aforementioned by-products (1) to (9) taken as the extending        agents;    -   the aforementioned compounds (10) to (21), (23) and (24) that        are taken as the strength adjusting agents;    -   (26) acetylpolybutyl citrate, or sugar-alcohols such as        glycerin, polyglycerin, propylene glycol, ethylene glycol, etc.,        and any mixture thereof.    -   Either one of the substances above or any mixture thereof may be        used.

The emulsifier is an additive to mix an oily additive adequately andemulsify the additive to be an oil-drop-in-water shape, provided thatthe oily additive is added to the molding material. Although the type ofthe emulsifier is not limited to any particular substance, what aretaken as the concrete examples are, for instance:

-   -   (27) surface active agents such as glycerin acid ester,        polyglycerin acid ester, propylene glycol fatty acid ester,        sugar ester, sorbitan acid ester, lecithin, polysorbate, etc.,        and any mixture thereof.    -   The stabilizer is an additive to stabilize the state of the        prepared molding material. Although the type of the stabilizer        is not limited to any particular substance, what are taken as        the concrete examples are, for instance: starch (in a narrow        sense, not modified) as the main material and a derivative        thereof; and    -   the substances taken as the strength adjusting agents such        as (10) saccharide, (11) sugar alcohol, (14) thickener        polysaccharide, (17) vegetable fibers and a derivative thereof        (except paper), and (21) fatty acid, fatty acid salts, and a        derivative of fatty acid etc. Either one of the substances above        and any mixture thereof may be used.

The homogeneity adjusting agent is an additive to make homogeneity inthe slurry or dough molding material, that is, “grain” of the slurry ordough molding material (in this case, grain, etc. of a solid matter inthe slurry or dough material) as fine, smooth and homogeneous aspossible. Although the homogeneity adjusting agent is not limited to anyparticular type, what are taken as the concrete examples are, forinstance:

-   -   Starch (in a narrow sense, not modified) as the main material,        or a derivative thereof; the aforementioned by-products (1)        to (9) taken as the extending agents;    -   the aforementioned components (10) to (25) taken as the strength        adjusting agents.    -   either one of the substances above and any mixture thereof may        be used.

The moisture retaining agent makes the expanded molded article contain acertain amount of water, and has the same effect as the plasticizer.That is to say, if the expanded molded article mainly made of starchincludes a certain amount of water (if moisture is retained), whilebrittleness of α-starch is decreased, strength and flexibility thereofare improved. Thus the moisture retaining agent can be used as aplasticizer and a strength adjusting agent as well.

The type of the moisture retaining agent is not limited to anyparticular substance either. What are taken as the concrete examplesare, for instance:

-   -   the starch (in a narrow sense, not modified) as the main        material and the derivative thereof;    -   the aforementioned by-products (1) to (9) taken as the extending        agents; and    -   the substances taken as the strength adjusting agents such        as (10) saccharide, (11) sugar alcohol, (12) fats and oils, (13)        waxes, (14) thickener polysaccharide, (15) metallic salts, (17)        vegetable fibers and their derivatives, (19) natural materials        such as a shell, bone powder, eggshell, leaf, wood powder, etc.,        and (22) food additives.    -   Either one of the substances above or any mixture thereof may be        used.

The handling adjusting agent works as a slurry adjusting agent and anadditive to improve handling of the slurry or dough molding material.Although the handling adjusting agent is not limited to any particularsubstance, all materials and compounds taken as the plasticizer,emulsifier, and stabilizer can be used. Either one of the substancesabove or any mixture thereof may be used.

The conductivity adjusting agent is an additive to adjust dielectricconstant of the molding material, which is one of the factors to controlthe heating state in case of internal heating as described later,especially in case of heat molding using internal heat generated byelectric heating, when the expanded molded article is molded. Althoughthe conductivity adjusting agent is not limited to any particular type,what are taken as the concrete examples are, for instance:

-   -   the substances taken as the strength adjusting agents such        as (12) fats and oils; (13) waxes; (14) thickener        polysaccharide; and (15) metallic salts; and (28) water soluble        electrolytes such as salts, acid, alkali, alcohol, etc.

Either one of the substances above or any mixture thereof may be used.

The dielectric loss adjusting agent is an additive to adjust adielectric loss of the molding material, which is one of the factors tocontrol the heating state especially in case of heating and moldingthrough internal heat generated by high frequency dielectric heating,when the expanded molded article is molded. Although the dielectric lossadjusting agent is not limited to any particular, what are taken as theconcrete examples are, for instance:

-   -   the substances that are taken as the strength adjusting agents        such as (12) fats and oils; (13) waxes; (15) metallic        salts; (16) insoluble minerals; and (17) vegetable fibers and        their derivatives;    -   the substances taken as the dielectric constant adjusting agent        such as (28) water soluble electrolytes; and (29) compounds        including zirconium salt such as zirconium salt, solution of        ammonium zirconium carbonate, etc., and any mixture thereof.

Either one of the substances above or any mixture thereof may be used.

The swelling agent is an additive to adjust the degree of expansion ofthe molding material and to further help swelling to form the expandedmolded article having an appropriate shape for the use. Although theswelling agent is not limited to any particular substance, what aretaken as the concrete examples are, for instance:

-   -   (30) organic swelling agents such as benzenesulfonyl hydrazine        compounds, azonitryl compounds, nitroso compounds, diazo        acetamide compounds, azocarboxylic acid compounds, etc. and        formulations including these agents;    -   (31) ammoniacal swelling agents such as espata, etc. and        formulations including these agents;    -   (32) inorganic swelling agents such as sodium bicarbonate,        ammonium alum hydrogen tartaric acid, magnesium carbonate, etc.        and formulations including these agents;    -   Either one of the substances above and any mixture thereof may        be used.

The coloring agent is an additive to color the whole expanded moldedarticle. Although the coloring agent is not limited to any particularsubstance, what are taken as the concrete examples are, for instance:

-   -   (33) inorganic pigments such as carbon black, etc.;    -   (34) natural or synthetic organic dyes such as colorants        specified by a color index;    -   (35) colorants made of natural materials such as caramel, cacao        powder, etc.    -   Either one of the substances above or any mixture thereof may be        used.

Among the additives in the molding material, it is preferable that thecontent of the extending agent (that may be termed as an extendingadditive) is not more than starch contained in the main solid matter ofthe molding material.

In the molding material of the present invention, water mixed withstarch of the main ingredient or a derivative thereof, is not limited toany particular type if it is water for industrial use.

The amount of added water in the above molding material is between 20weight % and 70 weight %, preferably between 25 weight % and 55 weight%, assuming that the molding material is taken as 100 weight %. Also,provided that various additives (functional additives) excluding themain solid matter (starch as the main material and extending agent) andthe extending agent (extensional additive) are collectively termedmaterial ingredients and total amount of the material ingredients in themolding material is taken as 100 weight %, the amount of added water inthe molding material is between 25 weight % and 230 weight %, preferablybetween 33 weight % and 120 weight %.

When the content of added water in the molding material is within theabove range, the molding material is in slurry or dough state. If thecontent of water in the molding material is less than 20 weight %, themolding material is scarcely fluid because of too small water content,which is not preferable in terms of molding. On the other hand, if thecontent of water is more than 70 weight %, the content of the solidmatter in the molding material becomes too low because of too largewater content, which is not preferable in terms of molding.

When the molding material is in slurry or dough state, moldability isimproved since it becomes easy to make the molding material fill acavity of the mold, as described later. It also becomes possible to makethe expanded molded article after molding contain a certain amount ofwater, and flexibility of the expanded molded article can be improved.

Next, the coating film 12 used in the present invention is described.

The coating film 12 is mainly made of biodegradable plastic and hashydrophobicity, that is, can impart water resistance to the expandedmolded article and can be softened and fused by heating. In addition, itis more preferable that the coating film 12 imparts gas impermeability,heat insulation, abrasion resistance, improved strength, andflexibility. Especially, when the biodegradable molded article inaccordance with the present invention is used for a highly hermeticstorage container, a gas impermeable coating film is highly preferable,since oxidation of, and moisture absorption by, the contents inside thecontainer must be avoided.

The material of the coating film 12 is not specifically limited as longas it is biodegradable and can impart water resistance and preferablygas impermeability to the expanded molded article after the film 12 isattached to the surface thereof.

More specifically, what are used as the materials are thoseconventionally known as biodegradable plastics such as 3-hydroxybutyricacid-3-hydroxyvaleric acid copolymer, poly-p-hydroxybenzaldehyde (PHB),polybutylene succinate (PBS), polycaprolactone (PLC), acetylcellulose(PH) polymer, polyethylene succinate (PESu), polyester amide, modifiedpolyester, polylactic acid (PLA), Mater-Bi (trademark of Novamont inItaly: having starch as the major component and biodegradable polyvinylalcohol resin and aliphatic polyester resin as the minor components),cellulose, and chitosan composite, etc. Either one of the materialsabove or any mixture thereof may be used. Also, accessory materials suchas a biodegradable plasticizer, filler, etc. may be added to thebiodegradable plastics.

It is preferable that the material of the coating film 12 is modifiedpolyester (where a structural unit easier to biodegrade than polyesteritself is inserted in a principal chain of polyester). Especially,sulfonic acid metallic salt is preferably inserted in a principal chainof aromatic saturated polyester. Also, biaxially stretched biodegradablefilm is preferably used as the coating film 12 due to its excellentstrength, heat resistance, and gas impermeability. Accordingly,double-axially denatured polyester is the most preferable as the coatingfilm 12.

In addition, the coating film 12 may be made by mixing starch to each ofthe above materials (biodegradable plastics). In this case, a mixingratio of the biodegradable plastic to starch is not specifically limitedunless various functions such as hydrophobicity of the coating film 12are degraded. For example an approximate mixing ratio of 1 to 1 byweight is preferably used.

Moreover, various additives are added to the coating film 12, forexample, colorants, additives for improving water resistance or gasimpermeability, additives for improving various characteristics ofsoftening at the time of attachment. However, additives are not limitedto any particular type.

Thickness of the coating film 12 (film thickness) is not specificallylimited if it is a film or a sheet within the range between 0.01 mm anda few millimeters before attaching to the expanded molded article.

In addition, since the coating film 12, as described below, is heated,softened and attached to the surface of the expanded molded article, itbecomes thinner than the above range after attachment. Thickness of thecoating film 12 after attachment is set so that the coating film 12 mayexert water resistance and gas impermeability, depending on the type ofbiodegradable plastics as the raw materials. The thickness is notspecifically limited, but preferably the maximum limit is not more than80 •m, more preferably not more than 50 •m. The minimum limit may be setso that the coating film 12 may exert water resistance and gasimpermeability as described above, In general, the minimum limit ispreferably not less than 5 •m.

Weight of the coating film 12 is preferably less than 40 weight % oftotal weight of the biodegradable molded article. Accordingly, it ispreferable to set the thickness of the coating film 12 to satisfy thisweight ratio. By minimizing amount of biodegradable plastics ofrelatively slow biodegrading speed, it is possible to exert a veryexcellent biodegradability as the whole biodegradable molded article.

The method to manufacture a biodegradable molded article in accordancewith the present invention is a method to mold a biodegradable expandedmolded article and the coating film 12 by pouring, heating andpressurizing the molding material and the coating film 12 inside themold, wherein an exhaust hole having a specific-shaped cavity(substantially same shape as the biodegradable molded article) isprovided, and after placing the coating film 12 in the mold, gaseousmatter between the coating film 12 and the surface of the mold isexhausted through the exhaust hole out of the cavity.

It is preferable that the mold consists of two or more dividable moldparts so that they can form a cavity matching with a shape of adesirable molded article inside by fitting the mold parts together andalso the expanded molded article can be removed after molding, and thatan exhaust hole to discharge gaseous matter inside the cavity outward ispierced in each of the mold parts. And in case that the biodegradablecontainer is manufactured as a biodegradable expanded molded article,the mold consisting of a concave mold part and a convex mold part to befit together is preferably used.

An example of the mold consisting of the concave mold part and theconvex mold part is a mold 20 a consisting of a pair of a metal convexmold part 21 a a metal concave mold part 22 a shown in FIG. 5( a) for abowl-shaped container.

The metal mold 20 a, as shown in FIG. 5 (b), forms a cavity 25 acorresponding to a shape of a desirable expanded molded article (referto FIG. 2) inside with the convex mold part 21 a and the concave moldpart 22 a fit together. By using the metal mold 20 a and placing themolding material inside the cavity 25 a between two coating films 12using the metal mold 20 a, the bowl-shaped container 10 a shown in FIG.2 is obtained.

Exhaust holes 31 a and 32 a to discharge gaseous matter inside thecavity 25 a outward pierce in each of the concave mold part 21 a and theconvex mold part 22 a. As shown in FIGS. 5 (a) and 5 (b), the exhaustholes 31 a and 32 a are provided on each of the positions correspondingto an upper end of a side wall 10 aa, a lower end of a side wall 10 aa,a concave part 10 af, an outer end of a foot 10 ad, an inner end of thefoot 10 ad, an outer end of a concave part 10 ae, a center of a concavepart 10 ae. The exhaust holes 31 a and 32 a are connected to the outsideof the metal mold 20 a through an outlet 34 a provided at a place otherthan a cavity forming part (a surface surrounding a cavity 25 a) on thesurface of the convex mold part 21 a and the concave mold part 22 a.

An insulator 27 to insulate the convex mold part 21 a and the concavemold part 22 a is provided at the fitting part (contacting part b) ofthe convex mold part 21 a and the concave mold part 22 a constitutingthe metal mold 20 a, which forms an electric field inside the metal mold20 a using the convex mold part 21 a and the concave mold part 22 a asan electrode and makes internal heating by electric conduction andinternal heating by dielectric heating (for example high-frequencydielectric heating) possible. Accordingly, as mentioned below, it ispossible to apply high-frequency dielectric heating by connecting ahigh-frequency power supply to the convex mold part 21 a and the concavemold part 22 a.

Another example of the mold consisting of the convex mold part and theconcave mold part is a metal mold 20 b for molding a round plate-shapedcontainer consisting of a pair of metal convex mold part 21 b and ametal concave mold part 22 b shown in FIG. 6 (a).

The metal mold 20 b, as shown in FIG. 6 (b), forms a cavity 25 b insidecorresponding to a shape of a desirable expanded molded article (referto FIG. 3) with the concave mold part 22 b and the convex mold part 22 bfit together (combined). By using the metal mold 20 b, placing themolding material inside the cavity 25 b between two coating films 12,and heating and pressurizing, a round plate-shaped container 10 b shownin FIG. 3 is obtained.

Exhaust holes 31 b and 32 b to discharge gaseous matter inside thecavity 25 b outward pierces each of the concave mold part 21 b and theconvex mold part 22 b. As shown in FIGS. 6( a) and 6 (b), the exhaustholes 31 b and 32 b are provided on each of the positions correspondingto an outer end of a flange 10 bc, an inner end of the flange 10 bc (anupper end of a curved part 10 ba), an outer end of a bottom 10 ba, acenter of the bottom 10 ba. The exhaust holes 31 b and 32 b lead to theoutside of the metal mold 20 b through an outlet 34 b provided at theplace other than a cavity-forming part (a surface surrounding a cavity25 b) on the surface of the convex mold part 21 b and the concave moldpart 22 b.

An insulator 27 to insulate the convex mold part 21 b and the concavemold part 22 b is provided at the fitting part (contacting part) of theconvex mold part 21 a and the concave mold part 22 a constituting themetal mold 20 b, which forms an electric field inside the metal mold 20a using the convex mold part 21 a and the concave mold part 22 a as anelectrode and makes internal heating by electric conduction and internalheating by dielectric heating (for example high-frequency dielectricheating) possible.

Diameter of the exhaust holes 31 a, 32 a and the exhaust holes 31 b and32 b can be small enough to give no effect on a surface of the coatingfilm 12 at all or at a practical level. In case that the shape of theexhaust holes (31 a and 32 a or 31 b and 32 b) the diameter ispreferably between 0.4 mm and 1.2 mm. In addition, the sectional area ofthe exhaust holes (31 a and 32 a or 31 b and 32 b) is preferably between0.12 mm² and 1.13 mm² without relation to the shape of the exhaustholes.

Diameter of parts 33 a and 33 b connecting the exhaust holes 31 a and 32a and exhaust holes 31 b and 32 b to the outlets 34 a and 34 b is notspecifically limited, but it is preferable that for smooth discharge, ithas a larger diameter than the exhaust holes 31 a, 32 a and exhaustholes 31 b and 32 b as shown in FIGS. 5 (a), 5(b), 6(a) and 6(b). Thatis to say, as shown in FIGS. 5( a), 5(b), 6(a) and 6(b), it ispreferable that the exhaust holes 31 a, 32 a and exhaust holes 31 b and32 b are connected to the outlets 34 a and 34 b by the exhaust holes 33a and 33 b having a larger diameter than that of the exhaust holes 31 a,32 a and exhaust holes 31 b and 32 b.

A knockout pin to take out the expanded molded article, a hinge, guideor a bar to movably link the convex mold parts 21 a and 21 b to theconcave mold parts 22 a and 22 b may be provided with the metal molds 20a and 20 b (not shown in drawings). The structure (position) of theexhaust tubes 33 a and 33 b and the outlets 34 a and 34 b are notspecifically limited. For example, the metal mold 20 a shown in FIGS. 5(a) and 5 (b) may be changed to the metal mold 20 a shown in FIG. 18.

Next, a heating method at the time of molding is described.

For the heating method at the time of molding, it is possible to useeither or both external heating to directly heat the mold by directheating means including direct heating, far-infrared radiation, electricheater, IH heating device, and/or internal heating to heat the moldingmaterial itself at the inside by internal heating means includingelectric heating, high-frequency dielectric heating and microwaveheating.

As the internal heating, high-frequency dielectric heating is the mostpreferable. Using high-frequency dielectric heating the molding materialheats up in a short time and is wholly expanded at once at the beginningof expanding and molding. Thus, pressure of the coating film pressed onthe mold occurs strongly and evenly. In result, it is possible to obtaina biodegradable molded article having higher adhesion of thebiodegradable expanded molded article to the coating film.

In case of internal heating, the molding material itself is heated.Therefore, the coating film 12 is heated by the high-temperature moldingmaterial during expanding and molding process and adhered to the surfaceof the expanded molded article. If internal heating is used, the coatingfilm 12 is not directly heated by the mold, which makes it possible touse the coating film 12 mainly made of a biodegradable plastic havingrelatively low melting point, for example, not more than 150° C. and toselect the coating film 12 more freely.

On the other hand, in the external heating, the coating film 12 isdirectly heated by the mold and the molding material placed inside isalso heated. Therefore, very high temperature is applied to the coatingfilm 12 to fully expand and mold the molding material. It is thuspreferable to use the coating film having higher melting point, and theheating temperature of the mold should be set more carefully consideringthe melting point or the softening point of the coating film.

From a point of view of easiness in attachment or selection of thecoating film 12, internal heating is more versatile as the heatingmethod.

However, external heating has an advantage that it is easier to controlsoftening of the coating film 12 or adhesion to the surface of theexpanded molded article, since the coating film 12 is directly heated bythe mold. In addition, in case that the coating film 12 has highsoftening point, when the molding material is heated by internal heatingto the extent that the coating film is fully softened, some varieties ofmolding material are excessively expanded and molded, resulting inpoorer quality of expanded molded article. In the cases, externalheating may be more preferable.

Thus, both external heating and internal heating have an advantage as aheating method, and both or either of external heating and/or internalheating may be selected depending what biodegradable molded article ismanufactured. Using both external heating and internal heating is themost preferable to take advantages of both heating methods.

In case of external heating, the mold (metal mold 20 a) is directlyheated by the direct heating means, whereby external heating is appliedto the molding material in the cavity (cavity 25 a) through the mold,and the molding material is molded into an expanded molded articlethrough steam expansion. In case of external heating only, it ispossible to eliminate the insulator 27 provided on the metal molds 20 aor 20 b.

On the other hand, in case of internal heating, for example, dielectricheating or electric heating, heating is performed by forming an electricfield using the convex mold part 21 a and the concave mold part 22 a asan electrode. For instance, as schematically shown in FIG. 8, it ispossible to use a heating device wherein the metal mold 20 a consistingof the convex mold part 21 a and the concave mold part 22 a is used, towhich the electrodes 26 and 26 are connected, respectively, and thepower supply 28 is connected to the electrodes 26 and 26. This can heatthe molding material to be filled in the cavity 25 a by internalheating. In case of high-frequency dielectric heating, high frequency isgenerated in the cavity 25 a as the power supply 28 using ahigh-frequency power supply, whereby the molding material filled in thecavity 25 a may be heated. Also, the electrode 26 is connected to thepower supply 28 as well as a switch or a control circuit (not shown).

It is possible to apply the structure that the electrode 26 is placed inthe convex mold part 21 a or the concave mold part 22 a, to the externalheating. That is, also in case of external heating, it is possible touse the structure that the direct heating means and the electrode 26 areprovided to directly heat the mold. Therefore, the structure shown inFIG. 8 that the electrode 26 is provided, can be used for both externalheating and internal heating.

As the internal heating, dielectric heating is especially preferable. Bydielectric heating, the molding material heats up in a short time at thebeginning of expanding and molding, and the entire molding materialexpands at once. This generates strong and even pressure that pressesthe coating film 12 on the metal mold. By controlling temperature of themold and heat generation of the molding material, it is possible toraise the temperature on an adhesive surface (surface adhered to thecoating film) on the expanded molded article until toward the meltingpoint, maintaining the temperature of a mold-contacting surface (surfacecontacting on the mold) on the coating film 12 below the melting point.In result, a biodegradable molded article which has high adhesiveness ofthe coating film 12 to the expanded molded article can be obtained.

The dielectric heating is a method to heat an object to be heated bydielectric loss of the object, including high-frequency dielectricheating which dielectrically heats the object (dielectric) by highfrequency (HF; 3 to 30 MHz) and microwave heating which dielectricallyheats the object (dielectric) by microwave (MW; 1 to 100 GHz).High-frequency dielectric heating is more preferable since dielectricheating can be performed using a metal mold made of metals as anelectrode and can accurately control an output device (high-frequencygenerator) to control heat generation of the molding material.

Next, an embodiment of a method to manufacture the biodegradable moldedarticle in accordance with the present invention is described in detailsbased on FIG. 1. Using the metal mold 20 a for molding a bowl-shapedcontainer shown in FIGS. 5 (a) and 5 (b), a case of manufacturing thebowl-shaped container 10 a is described in more detail as an example. InFIG. 1, to simplify the figure, only a part of the exhaust holes 31 aand 32 a in the metal mold 20 a are shown, but the other exhaust holes31 a and 32 a are not shown.

In a method to manufacture the biodegradable molded article inaccordance with the present invention, as shown in FIG. 1, a slurry ordough molding material 14 mainly made of starch or a derivative thereofand obtained by adding water thereto, and two coating films 12 mainlymade of biodegradable plastic and having hydrophobicity are used, themolding material 14 is placed between the coating films and pressurizedby the metal mold 20 a, to make the bowl-shaped container 10 a (refer toFIG. 2).

First, as shown in FIG. 1, the convex mold part 21 a and the concavemold part 22 a divided into two from the metal mold 20 a are placed sothat the center of the convex mold part 21 a and the concave mold part22 a is lined on a plumb line and the convex mold part 21 a and theconcave mold part 22 a is positioned upper and lower, respectively. Inaddition, a convex surface (lower surface) on the convex mold part 21 aand a concave surface (upper surface) on the concave mold part 22 a areopposed at substantially equal distance from any position along theplumb line.

Next, two coating films 12 that are not preformed, are placedsubstantially flat between the convex mold part 21 a and the concavemold part 22 a with the molding material 14. These two coating films 12are spaced and paralleled each other, and the slurry or dough moldingmaterial 14 is supplied between the two coating films 12. The coatingfilm 12 is placed vertically to a straight line connecting the center ofthe convex mold part 21 a with the center of the concave mold part 22 a.In this case, the coating film 12 is placed horizontally.

A method to position the coating film 12 substantially flat may be amethod to just pour the substantially flat coating film 12 into themetal mold 20 a or a method to fix the curled coating film 12 on bothsides of the metal mold 20 a. When the coating film 12 is put betweenthe convex mold part 21 a and the concave mold part 22 a, using aplurality of rollers placed on both sides of the metal mold 20 a, thecoating film can be continuously provided.

Then, by heating (pressurizing) and molding the molding material 14 andthe coating film 12 in the metal mold 20 a through the external heatingand/or internal heating, the molding material 14 is molded into the mainbody 11 a of the container through steam expansion, and at the sametime, the coating film 12 is softened and press-bonded (adhered) to thesurface of the main body 11 a.

At the time of heating and molding, the convex mold part 21 a is fit inthe concave mold part 22 a by moving at least either one of them,heating the molding material 14 and the coating film 12. Thus, thecoating film 12 starts to deform into a shape of the surface of theconvex mold part 21 a.

On the other hand, the molding material 14 is directly exposed to airuntil the convex mold part 21 a is fit in the concave mold part 22 a.So, the molding material 14 is maintained at relatively low temperature,which does not reach the lowest temperature at which steam expansionhappens (that is 100° C.). Even if steam expansion happens, the moldingmaterial 14 is maintained at relatively low temperature. Therefore,steam expansion of the molding material 14 does not happen at all, orslightly happens until the convex mold part 21 a is fit in the concavemold part 22 a.

Afterwards, when the convex mold part 21 a is fit in the concave moldpart 22 a and the metal mold 20 a is closed, the molding material 14 isblocked out from air and fully heated. Therefore, expansion by watercontained in the molding material 14 sufficiently goes off and themolding material 14 expands between the coating films 12. In result, themolding material 14 is molded as the main body 11 a, and at the sametime, the coating film 12 is pressed on the metal mold 20 a by themolding material 14 and molded into the substantially same shape as thesurface of the metal mold 20 a. Hence, it is possible to mold thebowl-shaped container 10 a into the shape corresponding to the cavity 25a, as the biodegradable molded article in accordance with the presentinvention.

In this case, soon after molding starts, air exists between the coatingfilm 12 and the surface of the metal mold 20 a. In the metal mold 20 ain this embodiment, the exhaust holes 31 a and 32 a for depressurizationare provided in the convex mold part 21 a and the concave mold part 22a. Therefore, air existing between the coating film 12 and the surfaceof metal mold 20 a is discharged outward through the exhaust holes 31 aand 32 a.

In result, air in the metal mold 20 a is substantially completelydischarged out of the cavity 25 a and the bowl-shaped container 10 a canbe molded into the substantially same shape as the cavity 25 a.

In the metal mold 20 a shown in FIGS. 5 (a) and 5 (b) or FIG. 18, thoughthe exhaust holes 31 a and 32 a lead to the outside of the metal mold 20a to discharge air in the cavity 25 a out of the metal mold 20 a, theexhaust holes 31 a and 32 a may lead to an enclosed space inside themetal mold 20 a. That is, an enclosed space leading to the cavity 25 athrough the exhaust holes 31 a and 32 a and shuts off the outside of themetal mold 20 a may be formed inside the metal mold 20 a. Moreparticularly, in the metal mold 20 a shown in FIG. 5 (a) and FIG. 5 (b),or FIG. 18, the outlet 34 a may be closed at the time of heating andmolding and an exhaust tube 33 a (a space inside the metal mold 20 aleading to the cavity 25 a through the exhaust holes 31 a and 32 a) maybe an enclosed space from the outside of the metal mold 20 a. In thiscase, air existing between the coating film 12 and the surface of themetal mold 20 a is discharged to an enclosed space through the exhaustholes 31 a and 32 a by the coating film 12 pressed by expansion of themolding material 14.

In result, as the case that the exhaust holes 31 a and 32 a lead to theoutside of the metal mold 20 a, air in the metal mold 20 a issubstantially completely discharged out of the cavity 25 a and thebowl-shaped container 10 a can be molded into the substantially sameshape as the cavity 25 a.

In addition, the method to use the metal mold 20 a forming such anenclosed space has an advantage that it is possible to easily avoiddeformation or tear of the coating film 12 due to a rapid increase ininner pressure of the cavity, in case that rapid molding is done or thecoating film 12 is not strong enough.

In the method to use the metal mold 20 a forming such an enclosed space,it is preferable that the volume of the enclosed space should be set atbetween a third and twice of the void volume in the cavity 25 a(capacity deducting the volume of the molding material 14 from thecapacity of the cavity 25 a) before heating and molding. It is possibleto avoid uneven thickness due to insufficient air exhaust by making thevolume of the enclosed space not less than a third of the void volumeinside the cavity 25 a before heating and molding. Also, it is possibleto avoid deformation or tear of the coating film 12 due to excessive airexhaust by making the volume inside the cavity 25 a not more than twiceof the void volume inside the cavity 25 a before heating and molding. Tosatisfy the volume ratio above, volume or form of the molding material14 may be adjusted, though adjusting size of the enclosed space in themetal mold 20 a is more convenient because the adjustment can be mademaintaining expansion rate consistently.

As mentioned above, in the method above, the exhaust holes 31 a and 32 afor depressurization are provided and air existing between the coatingfilm 12 and the surface of the convex mold part 21 a and the concavemold part 22 a are discharged out of the cavity 25 a through the exhaustholes 31 a and 32 a. This improves adhesiveness of the coating film 12to the surface of the convex mold part 21 a and the concave mold part 22a.

Therefore, in the above method, it is possible to avoid generation ofair bubbles on the surface of the coating film 12 and obtain thebowl-shaped container 10 a having excellent surface smoothness.Especially, since the surface of the flat area such as the side wall 10aa and the flange 10 ac becomes smooth, well-lustered and beautifulbowl-shaped container 10 a can be obtained.

In the method above, the bowl-shaped container 10 a can be molded intothe substantially same shape as the cavity 25 a with excellent accuracyof dimension. Especially, the coating film 12 is difficult to be adheredto the concave part of the surface on the metal mold 20 a, for example,a square of the bowl-shaped container 10 a (a square at the foot 10 ador the flange 10 ac), the concave part of the convex mold part 21 acorresponding to the convex part inside the bowl-shaped container 10 a(back side of the concave part 10 af), or a concave part of the concavemold part 22 a corresponding to the convex part (foot 10 ad) on theouter surface of the bowl-shaped container 10 a. However, in the methodabove, by discharging air existing between the coating film 12 and thesurface of the metal mold 20 a out of the cavity 25 a, it is possible toclosely adhere the coating film 12 also to the concave part on thesurface of the metal mold 20 a. In result, a corner, for example, at thefoot 10 ad and the flange 10 ac does not become rounded and forms apointed shape reflecting the shape of the cavity 25 a correctly. Also,it is possible to make thickness at the foot 10 ad and the concave part10 af of the bowl-shaped container 10 a substantially same as thicknessof the cavity 25 a.

In the method above, since air is discharged from the metal mold 20 ausing inner pressure in the metal mold 20 a generated by expansion ofthe molding material 14, air can be sufficiently discharged withoutvacuum suction. In this case, the diameter of the exhaust holes 31 a and32 a, as mentioned above, is small enough to make no influence on asurface of the coating film 12. Therefore, the convex partscorresponding to the exhaust holes 31 a and 32 a are not formed on thesurface of the coating film 12, but if any, there is no practicalinfluence.

In the manufacturing method in this embodiment, it is preferable tostraightly approximate the convex mold part 21 a and the concave moldpart 22, at least while the coating film 12 is deformed. In other words,it is preferable that a relative movement of the convex mold part 21 ato the concave mold part 22 is rectilinear motion. So more consistentpressure is applied to the coating film 12 by the convex mold part 21 a,compared with the case that a side of the convex mold part 21 a and aside of the concave mold part 22 is connected by a hinge and rotates theconvex mold part 21 a. Therefore, it is possible to extend the coatingfilm evenly and to make thickness of the coating film 12 uniform,thereby further improving effect by the coating film 12, that is, waterresistance of the biodegradable molded article.

Also, in the manufacturing method in this embodiment, it is preferableto move both convex mold part 21 a and concave mold part 22 a toapproximate each other at least until the coating film 12 starts todeform.

According to the method above, since both convex mold part 21 a and theconcave mold part 22 a are moved to approximate each other at leastuntil the coating film 12 starts to deform, the time necessary forfitting the convex mold part 21 a in the concave mold part 22 a (fittingtime) can be reduced, resulting in a reduction of the manufacturingtime.

Also, incase that the convex mold part 21 a and the concave mold part 22a are moved to approximate each other, both of the mold parts may bemoved to approximate each other until the convex mold part 21 a is fitin the concave mold part 22 a. However, it is preferable that bothconvex mold part 21 a and concave mold part 22 a are moved toapproximate each other until the coating film 12 starts to deform, whileonly the convex mold part 21 a is moved after the coating film starts todeform. This does not eliminate a necessity to move the coating film 12and makes operation easier when the coating film 12 is heldsubstantially flat, as the case that the coating film 12 is continuouslytransported.

Heating temperature of the metal mold 20 a at the time of heating andmolding may be within a range that can soften the coating film 12without fusion and pressure-bond it on the surface of the expandedmolded article, that is, not less than the softening point of thecoating film 12 and less than the melting point of the coating film 12,which is set preferably depending on thermal characteristics of thecoating film 12 used. Preferably, at the time of heating and molding,heating is performed so that the temperature of the metal mold 20 a maybe not less than the softening point of the coating film 12 and at least10° C. lower than the melting point thereof.

Accordingly the coating film 12 can be softened without fusion and aremolded into a shape corresponding to the metal mold 20 a, which canavoid pinholes on the coating film 12. Hence it is possible to moresecurely coat the main body 11 a of the container with the coating film12, thereby further ensuring water resistance of the bowl-shapedcontainer 10 a.

It is more preferable that at the time of heating and molding, heatingsatisfies a temperature condition that “the temperature of the metalmold 20 a is not less the softening point of the coating film 12, and atleast 10° C. lower than the melting point thereof and not less than 130°C. (hereinafter referred to as Temperature Condition A). This can fullyheat the slurry or dough molding material 14 in the cavity (cavity 25 aetc.) and mold it through steam expansion, which reduce molding timethrough steam expansion, make the conditions of steam expansion betterand obtain the main body 11 a with uniform and fine texture. Therefore,the manufacturing time can be reduced and the characteristic includingstrength of the bowl-shaped container 10 a can be improved.

It is more preferable that at the time of heating and molding, heatingsatisfies a temperature condition that “the temperature of the metalmold 20 a is not less than the softening point of the coating film 12and at least 10° C. lower than the melting point thereof and not lessthan 150° C. (hereinafter referred to as Temperature Condition B). Thiscan more fully heat the slurry or dough molding material 14 in thecavity (cavity 25 a etc.) and mold through steam expansion, which canfurther reduce the molding time through steam expansion, make theconditions of steam expansion much better, and obtain the main body 11 awith more uniform and fine texture. Therefore, the manufacturing timecan be further reduced and the characteristic including strength of thebowl-shaped container 10 a can be improved.

To satisfy the Temperature Condition A, it is necessary to use thecoating film 12 having the softening point of not less than 130° C. andthe melting point of not less than 140° C. To satisfy the TemperatureCondition B, it is necessary to use the coating film 12 having thesoftening point of not less than 150° C. and the melting point of notless than 160° C.

Using the coating film 12 having such softening point and melting pointcan not only satisfy the above temperature conditions but also obtainthe bowl-shaped container 10 a with high heat resistance that does noteasily cause softening or fusion. Especially, in case that thebowl-shaped container 10 a is used for a container of ready-to-servenoodles, it is possible to more certainly avoid deformation and fusionof the bowl-shaped container 10 a by heat such as hot water poured intothe bowl-shaped container 10 a.

Accordingly, as thermal characteristics of the coating film 12, it ispreferable to set a high heating temperature for the time of heating andmolding and to improve heat resistance of the bowl-shaped container 10a. More particularly, the softening point of the coating film 12 ispreferably not less than 120° C., and more preferably not less than 130°C., and still more preferably not less than 150° C. Also, the meltingpoint of the coating film 12 is preferably not less than 150° C., morepreferably not less than 170° C., and still more preferably not lessthan 200° C. Preferably the coating film 12 has the softening point ofnot less than 120° C. and the melting point of not less than 150° C.,more preferably the softening point of not less than 130° C. and themelting point of not less than 170° C. and the most preferably thesoftening point of not less than 150° C. and the melting point of notless than 200° C.

The maximum limit of temperature to heat the metal mold 20 a is notparticularly limited if it is less than the melting point of the coatingfilm 12. However, the temperature is preferably not more than 240° C. toavoid thermal changes of the bowl-shaped container 10 a.

Also, steam expansion molding is a molding method to bring air bubblesby evaporating water included in the molding material 14 and generatingsteam. In the manufacturing method in accordance with the presentinvention, it is necessary to heat the molding material 14 to thetemperature of boiling water of not less than 100° C. to mold themolding material 14 through steam expansion.

When external heating only is used as a heating method, heatingtemperature of the metal mold 20 a should be not less than 100° C. thatis the temperature of boiling water, more preferably sufficiently higherthan the temperature of boiling water, for example, not less than 140°C. This always evaporates water contained in the molding material 14into vapor and generates air bubbles. Accordingly, the resultant moldedarticle is always steam-expanded and the expanded molded article can beeasily obtained.

Therefore, if external heating is used as a heating method, it isnecessary to select the coating film 12 mainly made of a biodegradableplastic having the melting point of not less than 100° C. If the coatingfilm 12 is mainly made of a biodegradable plastic having the meltingpoint of less than 100° C., the coating film 12 is completely fused atthe temperature to fully mold the molding material 14 through steamexpansion and the coating film 12 can not maintain the film shape.

On the other hand, when internal heating only is used as a heatingmethod, or when both external heating and internal heating are used, themolding material 14 itself in the cavity (cavity 25 a etc.) isinternally heated by applying low-frequency alternating current orhigh-frequency electric field to the electrode 26. Accordingly, theheating temperature depends on various conditions relating to internalheating and is not particularly limited if it is not less than thetemperature that the molding material 14 is steam-expanded. Therefore,if internal heating is used, it is possible to use the coating film 12having the relatively lower melting point compared with externalheating.

Various conditions relate to internal heating. More particularly, thecharacteristics of the electrode 26 and scale of the low-frequencyalternating current and high-frequency electric field largely relate tointernal heating. In addition, as mentioned above, internal heatinglargely depends on conductivity or dielectric loss of the moldingmaterial 14. In other words, in case of heating and molding throughelectric conduction heating, the condition of heat generation iscontrolled by conductivity of the molding material 14. In case ofheating and molding through high-frequency dielectric heating, thecondition of heat generation is controlled by dielectric loss of themolding material 14. In practically, the various conditions are notparticularly limited if the temperature in the cavity is within the samerange as the external heating.

The heating time is set depending on heating temperature, shape orthickness of the main body 11 a, but it is preferable to set the time sothat water content of the main body 11 a after molding is at leastwithin a given range. In other words, it is preferable to set the timeso that moisture in the molding material 14 may not evaporate almostcompletely.

If the heating time is too long to the extent that moisture in the mainbody 11 a becomes smaller than the above range, the main body 11 a isexcessively expanded and does not have given water content. Therefore,the main body 11 a becomes rigid and brittle and undesirably degradesthe quality.

The heating time is not specifically limited. For example, in case ofhigh-frequency dielectric heating, molding can be completed in a muchshorter time compared with general external heating. Or if the main body11 a is thick, the heating time tends to be longer. Basically, theheating time is set depending on the heating method and the shape of themain body 11 a. In general, the heating time is preferably between 10seconds and 5 minutes.

Molding pressure at the time of heating and molding is not particularlylimited, but in general, preferably between 5 kg/cm² and 50 kg/cm². Ofcourse, it is possible to change the molding pressure depending onvarious conditions.

Also, in the manufacturing method of this embodiment, applying a slipagent on the surface of the metal mold 20 a contacting the coating film12. This can reduce contact fiction between the surface of the coatingfilm and the surface of the metal mold 20 a, and avoid damages such astears or cracks on the coating film 12 due to friction with the metalmold 20 a when the coating film 12 is drawn by the metal mold 20 a.

As the slip agent, it is possible to use an agent that can reducefriction between the surface of the metal mold 20 a and the surface ofthe coating film 12, such as generally called “lubricant” includinghigher aliphatic alcohols, fatty amides, metal soaps such as magnesiumstearate, fatty esters and compounds thereof, as well as fats and oilssuch as vegetable fat and oil, inorganic particles and fluoroplastics.The methods to apply the slip agent on the surface of the metal mold 20a include a method to apply liquid such as lubricants and fats and oilson the surface of the metal mold 20 a, a method to attach particles suchas inorganic particles on the surface of the metal mold 20 a, and amethod to form a solid layer of fluoroplastic on the surface of themetal mold 20 a. Among these methods, the method to form a solid layeron the surface of the metal mold 20 a is preferable. As the solid layerformed on the surface of the metal mold 20 a, a fluoroplastic layer ispreferable. So a fluoroplastic layer (fluoroplastic coating film, namelyfluoroplastic coating) formed on the surface of the metal mold 20 a isthe most preferable as the slip agent.

In case that a liquid slip agent is applied on the surface of the metalmold 20 a or in case that a particle-type slip agent is attached on thesurface of the metal mold 20 a, since these slip agents come off thesurface of the metal mold 20 a during molding, it is necessary to applythe slip agents every molding. On the other hand, if a fluoroplasticlayer is formed on the surface of the metal mold 20 a as a slip agent,the slip agent does not come off the surface of the metal mold 20 aduring molding and can be used for a long time. Accordingly, it ispossible to reduce labor to apply the slip agent on the surface of themetal mold 20 a.

In case that a liquid slip agent is applied or in case that aparticle-type slip agent is attached, since these slip agents attach tothe surface of the surface of the bowl-shaped container 10 a duringmolding, it is necessary to remove the slip agents after molding. On theother hand, in the method above, the slip agent does not attach to orstain the surface of the bowl-shaped container 10 a, so it is possibleto eliminate labor to remove the slip agent from the surface of thebowl-shaped container 10 a after molding.

The above fluoroplastic includes polytetrafluoro-ethylene (namelyTEFLON, registered trademark), tetra-fluoroethylene-hexafluoropropylenecopolymer, tetra-fluoroethylene-perfluoroalkyl vinyl ether copolymer,tetraethylene-ethylene copolymer, polytrifluoroethylene chloride,polyvinylidene fluoride. Polytetrafluoroethylene is especiallypreferable due to excellent heat resistance and lower cost.

Next, as another embodiment of the present invention, a method tomanufacture a round plate-shaped container 10 b is described based onFIG. 7. Also in FIG. 7, to simplify the drawing, only a part of theexhaust holes 31 b and 32 b in the metal mold 20 b is shown without theother exhaust holes 31 b and 32 b.

A method to manufacture the round plate-shaped container 10 b in thisembodiment is the same as the method to manufacture the bowl-shapedcontainer 10 a, except that the metal mold 20 b for molding the roundplate-shaped container consisting of the convex mold part 21 b and theconcave mold part 22 b shown in FIGS. 6 (a) and 6 (b) is used, insteadof the metal mold 20 a for the bowl-shaped container shown in FIGS. 5(a) and 5 (b).

That is to say, using the metal mold 20 b consisting of the convex moldpart 21 b and concave mold part 22 b, as shown in FIG. 7, the convexmold part 21 b and the concave mold part 22 b are placed in an upperposition and a lower position, respectively, and the molding material 14is placed between the convex mold part 21 b and the concave mold part 22b with a pair of coating films 12 placed in between. Then, the convexmold part 21 b and the concave mold part 22 b approach to each other andare fit and clamped together. Next, by heating and molding the moldingmaterial 14 and the coating film 12, the molding material 14 is moldedthrough steam expansion to obtain the main body 10 b, and at the sametime, the coating film 12 is softened and pressure-bonded on the surfaceof the main body 10 b. At the time of heating and molding, air existingbetween the coating film 12 and the surface of the metal mold 20 b isdischarged out of the metal mold 20 b through the exhaust holes 31 b and32 b provided in the convex mold part 21 b and the concave mold part 22b.

In the method above, the exhaust holes 31 b and 32 b fordepressurization are provided for the convex mold part 21 b and theconcave mold part 22 b. At the time of heating and molding, air existingbetween the coating film 12 and the surface of the convex mold part 21 band the surface of the concave mold part 22 b is discharged out of themetal mold 20 b through the exhaust holes 31 b and 32 b. This improvesadhesiveness of the coating film 12 to the surface of the convex moldpart 21 b and the concave mold part 22 b.

Therefore, in the method above, it is possible to avoid air bubbles onthe surface of the coating film 12 and to obtain the round plate-shapedcontainer 10 b having an excellent surface smoothness. Especially, asurface of flat areas such as the bottom 10 ba and the flange 10 bcbecomes smooth, which can make the well-lustered and beautiful roundplate-shaped container 10 b.

Also, in the method above, it is possible to mold the round plate-shapedcontainer 10 b into the substantially same shape as the cavity 25 b andto attain excellent accuracy in size. Especially, it is difficult toadhere the coating film 12 to the concave part on the surface of themetal mold 20 b, for example, a corner of the round plate-shapedcontainer 10 b (corner of the flange 10 bc). However, in the methodabove, it is possible to closely adhere the coating film 12 also on theconcave part on the surface of the metal mold 20 b by discharging airexisting between the coating film 12 and the surface of the metal mold20 b. In result, for example, the corner of the flange 10 bc is notrounded, but pointed accurately reflecting the shape of the cavity 25 b.Also, it is possible to make thickness of the round plate-shapedcontainer 10 b substantially same as thickness of the cavity 25 b.

Also in the method to manufacture the round plate-shaped container 10 b,as the method to manufacture the bowl-shaped container 10 a, an enclosedspace leading to the cavity 25 b through the exhaust holes 31 b and 32 band closed to the outside of the metal mold 20 b may be formed insidethe metal mold 20 b. More particularly, for example, in the metal mold20 b shown in FIGS. 6 (a) and 6 (b), at the time of heating and molding,the outlet 34 b may be closed and make the exhaust tube 33 b an enclosedspace from the outside of the metal mold 20 b. It is thus possible tomold the round plate-shaped container 10 b into substantially same shapeas the cavity 25 b and to have the same advantages as the method to usethe metal mold 20 a forming an enclosed space. It is preferable toadjust volume of the enclosed space to a range between a third and twiceof the capacity of gap inside the cavity 25 b before heating andmolding, from the same reason as the method to manufacture thebowl-shaped container 10 a.

In the description above, the metal mold 20 a for molding thebowl-shaped container and the metal mold 20 b for molding the roundplate-shaped container are explained as the mold in accordance with thepresent invention. Also, in the description above, the method tomanufacture the bowl-shaped container 10 a using the metal mold 20 a andthe method to manufacture the round plate-shaped container 10 b usingthe metal mold 20 b are explained as the manufacturing method inaccordance with the present invention. However, the mold in accordancewith the present invention may have another shape. The manufacturingmethod in accordance with the present invention may be a method tomanufacture a biodegradable molded article having another shape.

A mold having another shape in accordance with the present invention is,for example, a metal mold 20 c for molding a cup-shaped container shownin FIG. 9 (a) and FIG. 9 (b).

FIGS. 5 (a), 5 (b), 6 (a), 6 (b), 9 (a) and 9 (b) illustrate a molddividable into two in upper and lower position as a dividable mold.However, the method to divide a mold (that is, the number of mold parts)is not limited to the method to divide a mold into two in upper andlower position. For example, instead of the metal mold 20 b divided intotwo shown in FIGS. 9 (a) and 9 (b), it is possible to use the metal mold20 d for molding the cup-shaped container divided in three consisting ofa convex mold part 21 d having the same shape as the convex mold part 21c, and two concave mold parts 23 d and 24 d having a shape made bydividing the concave mold part 22 c in two, as shown in FIG. 10 (a).

When in the metal mold 20 c and the metal mold 20 d, the convex moldpart 21 c and the convex mold part 21 d are combined with the concavemold part 22 c and the concave mold parts 23 d and 24 d, respectively,as shown in FIG. 9 (b) and FIG. 10 (b), the cavities 25 a and 25 bshaped to a desirable expanded molded article (refer to FIG. 3) areformed the inside. Using the above metal mold 20 c or 20 d, as the caseof using the metal molds 20 a and 20 b, by placing the molding materialinside the cavity 25 c or 25 d between the coating films 12 andpressurizing and heating them, a main body 10 b of the cup-shapedcontainer shown in FIG. 4 can be obtained. Exhaust holes (not shown inthe figure) are in these metal molds 20 c and 20 d, as the metal molds20 a and 20 b.

Also, in this embodiment, the metal molds 20 a and 20 b are given as anexample of the mold in accordance with the present invention. Thisembodiment is not limited to this mold, and a mold made of conventionalvarious materials can be used. However, as described below, for the moldused in the present invention, heat resistance for steam expansionmolding, and at the same time, strength and abrasion resistance are alsorequired. In case of internal heating using a microwave, microwavepermeability is necessary. Accordingly, in case of internal heatingusing a microwave, a mold consisting of plastic and ceramic withmicrowave permeability, heat resistance, strength and abrasionresistance is preferable as the above mold. For the other cases,especially in case of internal heating using electric conduction andhigh-frequency dielectric, a mold consisting of metals, that is, “metalmold” is more preferable since the mold itself works as a part of anelectrode.

Moreover, in this embodiment, as an example of using a mold inaccordance with the present invention, a mold used in a method tomanufacture a biodegradable molded article wherein the molding materialand the coating film are heated and molded in the mold to mold thebiodegradable expanded molded article through steam expansion, and atthe same time, the coating film are softened and pressure-bonded on thesurface of the biodegradable expanded molded article, is described.However, the mold in accordance with the present invention can be usedwith no particular limitation if the biodegradable expanded moldedarticle is molded through steam expansion by internally heating a slurryor dough molding material mainly made of starch or a derivative thereofand obtained by mixing water therewith. Therefore, the mold inaccordance with the present invention can be used for a method to moldthe molding material only without the coating film.

In each of the methods above, the molding material is placed between twocoating films 12 for molding through steam expansion in the mold, andthe entire surface of the expanded molded article is coated with thecoating film 12. However, the coating film 12 is not necessarilyattached to the entire expanded molded article and can be attached onlyto the part that protects the expanded molded article. For example, aplate for purpose of temporarily placing a food on the surface, moreparticularly, a one-way plate whereon snack foods such as Takoyaki(octopus dumpling), Yakisoba (Japanese baked noodle), Okonomiyaki(Japanese pancake), hot dogs, and French fries are temporarily placed,eaten and disposed of, or a plate used as a setting for wrapping a cakeetc. may need some protection only on the surface (top surface of theplate). Accordingly, in case that the biodegradable molded article ismanufactured for such usage, the coating film 12 may coat only the topsurface of the expanded molded article.

In case that the biodegradable molded article in accordance with thepresent invention is used as cushioning materials used for packagingelectrical appliances, the coating film may be attached only to the partdirectly contacting on the electrical appliances. Especially, if theelectrical appliance is large, the cushioning materials become largerand an attaching mold to attach a coating film becomes larger. If thebiodegradable molded article is large, the coating film can be attachedto minimum requisite area.

On the other hand, in case that gas impermeability is required for theentire container so that not only boiling water may be poured in butalso dried noodles contained may not get oxidized or absorb moisture asa container for ready-to-serve noodles (bowl-shaped container shown inFIG. 2), it is preferable to attach the coating film on the entirecontainer.

In the method each of these embodiments above, heating and molding areperformed using the coating film 12 held substantially flat, whileheating and molding may be performed using the coating film 12 curvedcircularly.

Also, in the method each of these embodiments above, the flatly-formedcoating film 12 is used for heating and molding, while the coating filmsubstantially pre-shaped to the outline of the biodegradable moldedarticle may be used for heating and molding as Methods 1 to 6 below.

<Method 1>

Method 1 is a method to substantially pre-shape the coating film 12 usedto the outline of the biodegradable molded article in the methodexplained based on FIG. 1.

Some coating films 12 cannot be largely drawn at the time of molding,depending on the variety of biodegradable plastic of the mainingredient. In this method, by preparing a molding film that is thecoating film 12 preformed to a similar shape to the outline aftermolding, even if the coating film 12 which cannot largely drawn is used,the coating film can certainly and effectively coat more complicated andmore deep drawing-shaped expanded molded article. It is thus preferableto use for molding a biodegradable molded article of a rather deepdrawing shape, that is, enlarging in size vertically, as the bowl-shapedcontainer 10 a shown in FIG. 2.

As a method to mold the coating film 12, typical molding method of asheet film is used and is not particularly limited. For example, variousmolding methods including vacuum molding, injection molding and blowmolding are preferably used. The molding shape is not necessarily thesame to detail if it is almost the same as the shape of thebiodegradable molded article after molding. Since the coating film hassome flexibility, it may be shaped almost equally to the shape of thebiodegradable molded article after molding, namely, the shape of themold.

Particularly explaining Method 1, as shown in FIG. 11, two molding films12 a substantially pre-molded to the shape of the bowl-shaped container10 a are placed between the upper and lower mold parts 21 a and 22 a ofthe metal mold 20 a shown in FIGS. 5 (a) and 5 (b), and then the slurryor dough molding material 14 is supplied between these molding films 12a and 12 a. In this condition, the metal mold 20 a is heated to thetemperature less than the melting point of a biodegradable plastic thatis the main ingredient of the molding film 12 a (coating film 12).Afterwards, the upper mold part 21 a and the lower mold part 22 a arecombined, heated, pressurized and molded using the above externalheating and internal heating. By this one process, it is possible toobtain the bowl-shaped container 10 a (refer to FIG. 2) as thebiodegradable molded article in accordance with present invention.

<Method 2>

Method 2 is a method to perform the coating film 12 used into a bagshape, and to contain the molding material in the bag-shaped coatingfilm 12, in the method explained based on FIG. 7. This method can beespecially preferably used for molding the biodegradable molded articleenlarging in size horizontally in correspondence with the sheet-shapedcoating film 12, as the round plate-shaped container 10 b shown in FIG.2.

In this method, the coating film 12 is preformed into a bag shape tomake a package film to contain the molding material. When the moldingmaterial is put in the packaged film, it means the molding material issubstantially packaged in the package film and it is possible to preparea large amount of molding materials pre-portioned in the package filmand store them for a certain period of time. In addition, when thebiodegradable molded article is manufactured, molding is ready only bypouring the packaged materials into the mold at one time. Accordingly,this method has an advantage that the manufacturing process is furthersimplified.

The method to form the coating film 12 to a bag-shaped film is notparticularly limited. A conventional method to form a sheet- or afilm-shaped plastic into a bag shape is preferably used, for example,pillow packaging. The method to store the packaged materials that themolding material is portioned into the packaging film is notparticularly limited, too if a conventional storage method not todecompose starch is used.

In the present invention, the packaging film 12 b holding the moldingmaterial is “composition for expansion molding”. As described above,this composition for expansion molding (hereinafter referred to as amolding composition) not only can be prepared in multiple and stored fora certain period of time, but also can easily produce the biodegradablemolded article to which the coating film is attached, only by pouringthe composition into the mold and molding at one time. Accordingly, thecomposition is preferable to manufacture the biodegradable moldedarticle in an easy and convenient process.

Particularly explaining Method 2, as shown in FIG. 12, the coating film12 is preformed into a bag shape to make the packaging film 12 b. Theappropriate amount of molding material 14 is portioned into thepackaging film 12 b to prepare the molding composition 40 b. The moldingcomposition 40 b may be stored in a proper storage case. Then, themolding composition 40 b taken out of the storage case is placed on thelower mold part 22 b in the metal mold part 20 b shown in FIGS. 6 (a)and 6 (b). This is just ready for molding.

In this condition, the metal mold 20 b is heated to the temperature toless than the melting point of the biodegradable plastic that is themain ingredient of the coating film 12 (packaging film 12 b).Afterwards, the upper and lower mold parts 21 a and 22 b are combined,heated, pressurized and molded using the above external heating andinternal heating. By this one process, it is possible to obtain theround plate-shaped container 10 b (refer to FIG. 3) as the biodegradablemolded article in accordance with present invention.

<Method 3>

In Method 3, the coating film 12 used is preformed into a bag shape andsubstantially shaped to the outlines of the biodegradable moldedarticle. In other words, the packaging film 12 d in Method 2 is formedinto a molding packaging film further substantially shaped to theoutlines of the biodegradable molded article. This method can bepreferably used also for the biodegradable molded article having arelatively deep drawing shape, that is, vertically enlarging in sizesuch as the bowl-shaped container 10 a shown in FIG. 2.

The molding package film may be molded by pre-converting the coatingfilm 12 into a bag-shaped packaging film and then substantially shapingit to the outlines of the biodegradable molded article, or may beconverted into the package film after molding the coating film 12substantially shaped to the outlines. The molding method or the methodto convert to the package film is not particularly limited, and asmentioned above, conventional methods can be preferably used.

Particularly explaining Method 3, as shown in FIG. 13, the coating film12 is preformed into the molding package film 12 c. The appropriateamount of molding material is portioned into the molding package film 12c to prepare molding composition 40 c. The molding composition 40 c maybe stored in a storage case. Then, the molding composition 40 c takenout of the storage case is placed on the lower mold part 22 a of themetal mold 20 a shown in FIGS. 5( a) and 5 (b). This is ready formolding.

In this condition, the metal mold 20 a is heated to the temperature toless than the melting point of the biodegradable plastic that is themain ingredient of the coating film 12 (molding package film 12 c).Afterwards, the upper and lower mold parts 21 a and 22 a are combined,heated, pressurized and molded using the above external heating andinternal heating. By this one process, it is possible to obtain thebowl-shaped container 10 a (refer to FIG. 2) as the biodegradable moldedarticle in accordance with the present invention.

<Method 4>

Method 4 is a method to use the coating film 12 as a film piece cut intoa shape substantially shaped to the outlines of the biodegradable moldedarticle in Method 1. This method can be preferably used for thebiodegradable molded article having a deep drawing shape or a morecomplicated shape such as the cup-shaped container 10 c shown in FIG. 4.

The shape of the film piece is not particularly limited, but in general,as shown in FIGS. 14 (a) and 14 (b), a method to make a plurality offilm pieces made by cutting each face in a rough development elevationof the biodegradable molded article after molding (for example, thecup-shaped container 10 c) is preferably used.

The film pieces 12 d have an overlap section 12 e equivalent to anoverlapped width as shown in FIGS. 14 (a) and 14 (b). The overlapsection 12 e is provided around the film pieces 12 d as the bottom, orat the end bonded when the film pieces 12 d as the side arecylindrically rolled.

At the overlap section 12 e, the film pieces 12 d are overlapped at agiven position of each of the film pieces 12 d when they are placed inthe cavity of the mold. This softens and bonds (fuses) the overlapsection 12 e and a part of the film pieces 12 d overlapped thereon atthe time of molding. In result, the substantially cup-shaped coatingfilm 12 is formed by putting together a plurality of film pieces 12 d.The coating film 12 is further attached to the surface of the expandedmolded article, resulting in the cup-shaped container 10 c in accordancewith the present invention.

The shape of the film pieces 12 d as the rough development elevation isnot particularly limited. As an example, in case of making thecup-shaped container 10 c, as shown in FIG. 14 (a), two film pieces 12 dmay correspond to the side face and the bottom face by dividing thedevelopment elevation into two, or three film pieces 12 d may correspondto one bottom face and two side faces by dividing the developmentelevation into three, as shown in FIG. 14 (b). As mentioned above, thefilm pieces 12 d are shaped in correspondence with the cup-shapedbiodegradable molded article etc. with all the film pieces 12 doverlapped at the overlap section 12 e.

In this method, the coating film 12 before attachment is further formedinto a shape after molding compared with Method 1 or Method 3.Therefore, in case of using the coating film 12 mainly made of abiodegradable plastic having poor drawability, especially, in case ofmolding the biodegradable molded article of deep drawing shape such asthe cup-shaped container 10 c with the coating film 12 of poordrawability, or in case of optionally adjusting thickness of the coatingfilm 12 after attachment, this method can be effectively used.

Explaining the Method 4 more particularly, as shown in FIG. 15, in themetal mold 20 d shown in FIGS. 10 (a) and 10 (b), the film pieces 12 dcorresponding to the bottom face of the cup-shaped container 10 c andthe film pieces 12 d corresponding to the side face are placed along theshape of the cavity of the lower mold parts 23 d and 24 d. Theoverlapped part 12 e is completely overlapped.

Then, the molding material 14 is further supplied on the film piece 12 dshaped to the substantial cup shape. On the other hand, the film piece12 d corresponding to the bottom face of the cup-shaped container 10 cand the film piece 12 d corresponding to the side face are placed inaccordance with the shape of the upper mold part 21 d. The upper moldpart 21 d is fit in the lower mold parts 23 d and 24 d together with thefilm pieces 12 d. Of course, these mold parts 21 d, 23 d and 24 d areheated up to the temperature less than the melting point of thebiodegradable plastic that is the main ingredient of the coating film12.

Afterwards, heating, pressurizing and molding are done using the aboveexternal heating and internal heating. At the time of this heating,pressurizing and molding, a layer of the coating film 12 is formed onthe surface of the expanded molded article (main body 11 c) with no gapby fusing the overlap section 12 e of the film pieces 12 d. In result,by this one process, the cup-shaped container 10 c as the biodegradablemolded article in accordance with the present invention can be obtained.(Refer to FIG. 4.)

<Method 5>

In Method 5, based on Method 4, the film pieces 12 c are adhered on theoverlap section 12 e and pre-formed to almost conform to the outlines ofthe biodegradable molded article before molding. This method can bepreferable used for molding the biodegradable molded article of a deepdrawing shape or more complicated shape such as the cup-shaped containershown in FIG. 4.

This method is basically the same as Method 4. The overlap sections 12 dand 12 d are securely adhered through fusion to pre-form an outlinefilm. This is an effective method in case of using the coating film 12that is difficult to fuse the overlap sections 12 d and 12 d in theabove method 4 at one-time molding.

Explaining Method 5 more particularly, as shown in FIG. 16, in the metalmold 20 d shown in FIGS. 10 (a) and 10 (b), the outline films 12 f thatare adhered in advance in the substantial cup shape are placed in twopiles between the upper and lower mold parts 21 d, 23 d and 24 d, andthe molding material is supplied between the outline films 12 f and 12f. In this condition, the metal mold 20 b is heated up to thetemperature less than the melting point of the biodegradable plasticthat is the main ingredient of the outline film 12 f (coating film 12).Afterwards, the upper and lower mold parts 21 c, 23 d and 24 d are fittogether, heated, pressurized and molded using the external heating orinternal heating. By this one process, it is possible to obtain thecup-shaped container 10 c as the biodegradable molded article inaccordance with the present invention (refer to FIG. 4).

<Method 6>

Method 6 is a method to combine Method 2 with Method 5. That is to say,the film pieces 12 c are adhered at the overlap section 12 d to almostconform to the outlines of the biodegradable molded article beforemolding. Then, the overlapped film pieces are converted to a substantialbag shape wherein the molding material is portioned. This method can bepreferably used for molding the biodegradable molded article of a deepdrawing shape and more complicated shape such as the cup-shapedcontainer 10 c shown in FIG. 4, as Method 4 or Method 5.

Also in this method, as Method 2 and Method 3, the coating film 12 ispreformed into a package film and the molding composition is preparedwherein the molding material is contained. So, the molding compositioncan be stored for a certain period of time and molding is ready only bypouring the molding composition in the mold at one time, thereby furthersimplifying the manufacturing process.

Explaining Method 6 more particularly, as shown in FIG. 17, the coatingfilm 12 is formed into a film piece in correspondence with the outlinesof the cup-shaped container 10 c, and the film pieces are bondedtogether and formed into the outline film. In addition, two of theoutline films are bonded together and converted into the bag-shapedoutline packaging film 12 g. An approximate amount of molding material14 is portioned in the outline packaging film 12 g to prepare themolding composition 40 g. The molding composition 40 g may be stored ina given storage case. Then, in the metal mold 20 d shown in FIGS. 8 (a)and (b), the substantial cup-shaped molding composition 40 g taken outof the storage case are placed on the lower mold parts 23 d and 24 d.This is just ready for molding.

In this condition, the metal mold 20 d is heated up to the temperatureof less than the melting point of the biodegradable plastic that is themain ingredient of the coating film 12 (outline packaging film 12 g).Afterwards, the upper and lower mold parts 21 d, 23 d and 24 d are fit,heated, pressurized and molded using the external heating and internalheating. By this one process, it is possible to obtain the cup-shapedcontainer 10 c as the biodegradable molded article in accordance withthe present invention (refer to FIG. 4).

Embodiment 2

An embodiment of the present invention is described below based on FIG.20 to FIG. 24. The present invention is not limited to this embodiment.For convenience of explanation, the members having the same function aseach member shown in the above embodiment 1 have the same code with noexplanation.

First, a biodegradable molded article manufactured by a method of thisembodiment has a structure that a coating film is formed directly on asurface of an expanded molded article, as the biodegradable moldedarticle manufactured by the method of Embodiment 1.

The method of this embodiment is a method to manufacture a biodegradablemolded article of a deep drawing shape, or a method suitable tomanufacture a biodegradable molded article of a deep drawing shape.

The biodegradable molded article of a deep drawing shape is, forexample, the bowl-shaped container 10 a shown in FIG. 2 explained inEmbodiment 1, an almost similar bowl-shaped container such as thebowl-shaped container 10 a shown in FIG. 21, or a cup-shaped containersuch as the cup-shaped container 10 c show in FIG. 4 explained in theembodiment 1.

The method to manufacture a biodegradable molded article in accordancewith this embodiment, is a method to manufacture the biodegradablemolded article of a deep drawing shape that a slurry or dough moldingmaterial mainly made of starch or a derivative thereof and obtained bymixing water therewith, and a coating film mainly made of abiodegradable plastic and having hydrophobicity are used, the coatingfilm is placed substantially flat with the molding material in the moldof a deep drawing shape, and at the same time, the coating film issoftened and pressure-bonded on the surface of the expanded moldedarticle.

The method to manufacture the biodegradable molded article in accordancewith this embodiment is a method to mold the molding material throughsteam expansion and at the same time to directly attach the coating filmto the expanded molded article. Accordingly, as Embodiment 1, thisembodiment has above-mentioned four advantages compared with the afterattaching method. It is thus possible to manufacture the biodegradablemolded article efficiently, at low cost, and easy to use for disposablepurpose.

The molding material and the coating film used in this embodiment is thesame as those used in Embodiment 1.

The desirable molding method in this embodiment is a method to use amold of a deep drawing shape having a cavity conformed to a shape of adesirable molded article and consisting of at least two parts and moldthe expanded molded article and the coating film by pouring, heating andpressurizing the molding material and the coating film in the cavity ofthe mold.

Therefore, the mold of a deep drawing shape may have a cavity conformedto a shape of a desirable molded article and be equipped with at leasttwo metal mold parts dividable to remove the expanded molded articleafter molding. Incase that the biodegradable container is manufacturedas the biodegradable expanded molded article, a mold consisting of ametal convex mold part (convex mold) and a metal concave mold part(concave mold) fit in each other is preferably used.

The mold of a deep drawing shape consisting of the convex mold part anda concave mold part includes, for example, the metal mold 20 aconsisting of a pair of the metal convex mold part (convex mold) 21 aand the metal concave mold part (concave mold) 22 a shown in FIG. 22(a), the metal mold similar to the metal mold 20 c shown in FIG. 9 (a)except that an exhaust hole which is not shown in FIG. 9 (a) is notprovided, and the metal mold similar to the metal mold 20 c shown inFIG. 10 (a) except that an exhaust hole that is not shown in FIG. 10 (a)is not provided.

The metal mold 20 a shown in FIG. 22 (a) is in a combined condition ofthe convex mold part 21 a and the concave mold part 22 a, wherein thecavity 25 a conformed to the shape of the desirable expanded moldedarticle (refer to FIG. 21) is formed as shown in FIG. 22 (b).

The metal mold 20 a shown in FIG. 22 (a) is equipped with the samestructure as that of the metal mold 20 a shown in FIG. 5 (a), exceptthat the exhaust holes 31 a ad 32 a, exhaust tube 33 a, outlet 34 a andinsulator 27 are not provided, and that the shape of the cavity 25 a isa little different.

In addition, the heating method at the time of molding in thisembodiment is the same as Embodiment 1. As a method to internally heatthe molding material supplied in the cavity 25 a, as schematically shownin FIG. 24, it is possible to use a heating device using the metal mold20 a consisting of the convex mold part 21 a and the concave mold part22 a, connecting the electrodes 26 and 26 to the convex mold part 21 aand the concave mold part 22 a, respectively, placing an insulator 27 ata contacting part with the convex mold part 21 a and the concave moldpart 22 a, and connecting the electrodes 26 and 26 to the power supply28.

Next, an embodiment of a method to manufacture a biodegradable moldedarticle of a deep drawing shape in accordance with the present inventionis described based on FIG. 20. The case that the bowl-shaped container10 a is manufactured using the bowl-shaped metal mold 20 a consisting ofthe convex mold part 21 a and the concave mold part 22 a shown in FIG.22 (a), is described in more detail as an example.

First, as shown in FIG. 20, the convex mold part 21 a and the concavemold part 22 a of the metal mold 20 a divided into two are placed sothat the center of the convex mold part 21 a and the center of theconcave mold part 22 a may be aligned on plumb line and the convex moldpart 21 a and the concave mold part 22 a may be arranged in an upper andlower position, respectively, as Embodiment 1.

Next, two coating films 12 that are not preformed, are placedsubstantially flat with the molding material 14 between the convex moldpart 21 a and the concave mold part 22 a as Embodiment 1.

Then, as Embodiment 1, by heating and (pressurizing) molding the moldingmaterial 14 and the coating film in the metal mold 20 a using the aboveexternal heating and/or internal heating, the main body 11 a is moldedthrough steam expansion and at the same time, the coating film 12 issoftened and pressure-bonded (adhered) to the surface of the main body11 a. By this one process, the bowl-shaped container 10 a can be moldedas the biodegradable molded article in accordance with the presentinvention.

When heating and molding the molding material 14 and the coating film12, at least either one of the convex mold part 21 a and the concavemold part 22 a is moved to the direction where the convex mold part 21 ais fit in the concave mold part 22 a. Therefore, as shown in FIG. 23(a), the convex mold part 21 a contacts the center part of the uppercoating film 12, which starts to deform by pressure from the convexmold. Then, the center part of the coating film 12 is deforming to ashape of the surface of the convex mold part 21 a as shown in FIG. 23(b), finally to the shape substantially same as the surface of theconvex mold part 21 a when the convex mold part 21 a is fit in theconcave mold part 22 a. In FIG. 23 (a) and FIG. 23 (b), the coating film12 is only shown for simplification of the drawing.

As mentioned above, the center part of the coating film 12 is deformedand molded by pressure from the convex mold part 21 a. Since the convexmold part 21 a has a deep drawing shape, the coating film issignificantly drawn. Accordingly, it is important to optimize the speedof drawing the coating film 12.

The speed of drawing the coating film 12 depends on a relative movingspeed of the convex mold part 21 a to a fixed surface A (refer to FIG.23 (b)) of the coating film 12 while the coating film 12 is beingdeformed. The fixed surface A of the coating film is a flat face formedby connecting parts that are not deformed on an outer periphery of thecoating film 12 (in this case, a fixed part of an upper part of theconcave mold part 22 a).

In the method of this embodiment, it is preferable to maintain therelative moving speed of the convex mold part 21 a to the fixed surfaceA of the coating film within 8 mm/s to 12 mm/s, at least while thecoating film 12 is being deformed.

This can maintain the speed of drawing the coating film 12 by the convexmold part 21 a almost consistently and at an optimal speed. It is thuspossible to avoid any tears, cracks or pinholes on the coating film 12.If the relative moving speed of the convex mold part 21 a to the fixedsurface A of the coating film is faster than 12 mm/s, some splits orcracks may be caused more often because the coating film 12 is drawnrapidly. On the contrary, if the relative moving speed of the convexmold part 21 a to the fixed surface A of the coating film is slower than8 mm/s, some pinholes may be caused more often due to some unclearreasons.

Especially, in the manufacturing method of this embodiment, since themolded article of a deep drawing shape (bowl-shaped container 10 a) ismanufactured using the substantially flat coating film 12, the coatingfilm 12 is significantly drawn. In case that a biaxially stretched filmhaving especially excellent heat resistance and gas impermeability isused as the coating film 12, it is relatively difficult to draw thecoating film 12 not to cause tears, cracks or pinholes on the coatingfilm 12. However, by setting the moving speed within the above range, itis possible to avoid tears, cracks or pinholes also in the above case.In result, the main body 11 a can be more securely coated by the coatingfilm 12 and can ensure water resistance of the bowl-shaped container 10a more certainly.

In the method of this embodiment, since the outer periphery of thecoating film 12 is fixed at the upper part of the concave mold part 22a, the fixed surface A of the coating film is at a given distance fromthe upper surface of the concave mold part 22 a. Therefore, the relativemoving speed of the convex mold part 21 a to the fixed surface A of thecoating film is equal to the relative approach speed of the convex moldpart 21 a and the concave mold part 21 a. On the other hand, it ispossible to fix the outer periphery of the coating film 12 using anotherfixing means, instead of fixing the outer periphery of the coating film12 on the upper end of the concave mold part 22 a as this embodiment. Inthe case, the relative moving speed of the convex mold part 21 a to thefixed surface A of the coating film is not equal to the relativeapproach speed of the convex mold part 21 a and the concave mold part 21a, but equal to the relative moving speed of the convex mold part 21 aand the fixing means.

Also, in this embodiment, the period of time when the coating film 12 isdeformed, is from the time when the coating film 12 starts to deform bypressure from the convex mold part 21 a (when the convex mold part 21 ashown in FIG. 23 (a) first contacts the upper coating film 12) throughthe time when the coating film 12 is molded to the substantially sameshape as the surface of the convex mold part 21 a (when the convex moldpart 21 shown in FIG. 23 (b) is fit in the concave mold part 22 a).

The above range of the relative moving speed is based on an experimentusing the coating film 12 having a thickness of 20 to 80 •m. However,also in case that the coating film of the other thickness, it isestimated that almost the same result as the case of using the coatingfilm 12 having a thickness of 20 to 80 •m may be obtained by setting theabove range of the relative moving speed of the convex mold part 21 a tothe fixed surface A of the coating film.

In the method of this embodiment, it is preferable to straightlyapproximate the convex mold part 21 a and the concave mold part 22, atleast while the coating film 12 is deformed. That is to say, it ispreferable that the relative movement of the convex mold part 21 a tothe concave mold part 22 is a linear motion.

According to the method above, for example, compared with the case thatone side of the convex mold part 21 a is joined with one side of theconcave mold part 22 with a hinge to rotate the convex mold part 21 a,pressure applied to the coating film 12 by the convex mold part 21 abecomes more consistent. Thus, it is possible to draw the coating film12 consistently and make the thickness of the coating film 12 uniform.Therefore, an effect by the coating film 12, that is, water resistanceof the biodegradable molded article is further improved.

In the method of this embodiment, in case that the relative moving speedof the convex mold part 21 a to the fixed surface A of the coating filmis maintained within 8 mm/s to 12 mm/s while the coating film 12 isdeformed, the period of time from when the coating film 12 starts todeform through the time when the convex mold part 21 a is fit in theconcave mold part 22 a, is limited to a specific range depending on theshape of the metal mold 20 a. On the other hand, the relative movingspeed of the convex mold part 21 a to the fixed surface A of the coatingfilm until the coating film 12 starts to deform can be optionally set.

In the method of this embodiment, it is preferable to approximate bothof the convex mold part 21 a and the concave mold part 22 a to eachother at least until the coating film 12 starts to deform.

According to the method above, since both of the convex mold part 21 aand the concave mold part 22 a are moved to approximate each other, itmakes the time (fitting time) shorter necessary to fit the convex moldpart 21 a and the concave mold part 22 a, thereby reducing themanufacturing time.

In case that both of the convex mold part 21 a and the concave mold part22 a are moved to approach to each other, both of the convex mold part21 a and the concave mold part 22 a may be moved to approximate eachother until the convex mold part 21 a is fit in the concave mold part 22a. However, it is preferable that the convex mold part 21 a only ismoved after the coating film 12 starts to deform, while the both of theconvex mold part 21 a and the concave mold part 22 a are moved toapproach to each other until the coating film 12 starts to deform. Thiseliminates the necessity to move the coating film 12, when the coatingfilm 12 is held substantially flat as the case of transporting thecoating film 12 continuously surface.

Heating temperature of the metal mold 20 a, various conditions relatingto internal heating, heating time and molding pressure at the time ofheating and molding is the same as Embodiment 1.

In other words, it is preferable that the metal mold 20 a is heated atnot less than the softening point of the coating film 12 and at least10° C. lower than the melting point thereof at the time of heating andmolding.

It is thus possible to soften and mold the coating film 12 into a shapecorresponding to the metal mold 20 a without melting and to avoidpinholes on the coating film 12. Since it is possible to more securelycoat the main body 11 a with the coating film 12, thereby furtherensuring water resistance of the bowl-shaped container 10 a.

Also, to reduce manufacturing time and improve the characteristicsincluding strength of the bowl-shaped container 10 a, it is morepreferable Temperature Condition A that “the temperature of the metalmold 20 a is not less than the softening point of the coating film 12,and at least 10° C. lower than the melting point thereof and at leastmore than 130° C. is satisfied. It is still more preferable temperaturecondition that” the temperature of the metal mold 20 a is not less thanthe softening point of the coating film 12, at least 10° C. lower thanthe melting point thereof and not less than 150° C. (hereinafterreferred to as Temperature Condition B) is satisfied.

Thermal characteristics of the coating film 12 necessary to satisfy theabove Temperature Condition A or B is the same as Embodiment 1. In otherwords, to satisfy Temperature Condition A, it is necessary to use thecoating film 12 whose softening point is not less than 130° C. andmelting point is not less than 140° C. To satisfy Temperature ConditionB, it is necessary to use the coating film 12 whose softening point isnot less than 150° C. and melting point is not less than 160° C.

It is preferable that the coating film 12 has thermal characteristics toset a higher heating temperature at the time of heating and molding andto improve heat resistance of the bowl-shaped container 10 a asEmbodiment 1. More particularly, the softening point of the coating film12 is preferably not less than 120° C., more preferably not less than130° C., and still more preferably not less than 150° C. The meltingpoint of the coating film 12 is preferably not less than 150° C., morepreferably not less than 170° C., and still more preferably not lessthan 200° C. Also, preferably the coating film 12 has the softeningpoint of not less than 120° C. and the melting point of not less than150° C., more preferably, the softening point of not less than 130° C.and the melting point of not less than 170° C., and the most preferably,the softening point of not less than 150° C. and the melting point ofnot less than 200° C.

In the manufacturing method of this embodiment, it is preferable that aslip agent is applied to a surface of the metal mold 20 a contacting thecoating film 12. This can reduce contact friction between the surface ofthe coating film 12 and the surface of the metal mold 20 a, and to avoiddamages including tears and cracks on the coating film 12 due tofriction with the metal mold 20 a when the coating film 12 is drawn bythe metal mold 20 a.

The type of the slip agent and method to apply on the surface of themetal mold 20 may use the example in Embodiment 1. From the abovereason, it is preferable to form a solid layer on the surface of themetal mold 20 a. The solid layer formed on the surface of the metal mold20 a is preferably a fluoroplastic layer. Therefore, it is the mostpreferable that the slip agent is a fluoroplastic layer (fluoroplasticcoating) formed on the surface of the metal mold 20 a. The fluoroplasticexampled in Embodiment 1 may be used, but tetrafluoroethylene isespecially preferably from the above-mentioned reason.

As mentioned above, the manufacturing method of this embodiment is amethod to use the slurry or dough molding material 14 mainly made ofstarch or a derivative thereof and obtained by adding water thereto andthe coating film mainly made of a biodegradable plastic and havinghydrophobicity, place the molding material 14 and the coating film 12substantially flat in the metal mold 20 a of a deep drawing shape, moldthe main body 11 a through steam expansion by heating and molding themolding material 14 and the coating film 12 in the metal mold 20 a, andat the same time, soften and pressure bond the coating film 12 to asurface of the main body 11 a to make the bowl-shaped container 10 a.

The manufacturing method of this embodiment is a method to use the metalmold 20 a consisting a pair of the convex mold part 21 a and the concavemold part 22 a, place the molding material 14 and the coating film 12between the convex mold part 21 a and the concave mold part 22 a beforeheating and molding, deform the center part of the coating film 12 bymoving at least either one of the convex mold part 21 a and the concavemold part 22 a to a direction where these mold parts are fit together atthe time of heating and molding, and to maintain the relative movingspeed of the convex mold part 21 a to the fixed surface A of the coatingfilm formed by connecting a surface of non-deforming parts on the outerperiphery of the coating film 12 within the range of 8 mm/s to 12 mm/s.

Also, the manufacturing method of this embodiment is a method whereinheating is performed so that the temperature of the metal mold 20 a isnot less than the softening point of the coating film 12 and 10° C.lower than the melting point thereof at the time of heating and molding.

In the method above, the case of manufacturing the bowl-shaped container10 a using the metal mold 20 a is explained. It is also possible tomanufacture a biodegradable molded article having another shape such asthe cup-shaped container 10 b by a metal mold having another deepdrawing shape including the metal molds 20 b and 20 c.

Though the method above is especially suitable to manufacture abiodegradable molded article of a deep drawing shape, the heating methodunder the above conditions is also useful to manufacture a biodegradablemolded article horizontally enlarging in size, such as the plate-shapedcontainer 10 b.

In the method above, the convex mold part 21 a and the concave mold part22 b are placed in an upper position and a lower position, respectively.However, the concave mold part 22 b and the convex mold part 21 b can beplaced in an upper position and a lower position, respectively. In thisembodiment, the convex mold part 21 b and the concave mold part 22 b areplaced in an upper position and a lower position, respectively, and theymove vertically. However, placement and moving direction is notespecially limited and may be moved horizontally.

In the method above, for molding steam expansion molding in the mold,the molding material is inserted between two coating films 12 which coatthe entire surface of the expanded molded article. However, in thepresent invention, the coating film may coat the upper part only of theexpanded molded article.

On the other hand, for example, as a container for ready-to-servenoodles (the bowl-shaped container 10 a shown in FIG. 21 etc.), in casethat gas impermeability is required for the entire container not only topour boiling water in and but also to avoid oxidation or moistureabsorption of dried noodles contained, it is preferable to attach thecoating film 12 on the whole container.

Next, the present invention is described in more detail based onexamples and comparative examples, however, the present invention is notlimited to these examples.

(Molding Material)

Various types of starch as the main ingredient (including a derivativethereof), additives and water are uniformly mixed by a mixer to makecompositions shown in Table 1 and to prepare slurry molding materials(1) to (3) and dough molding materials (4) to (6) and (8).

TABLE 1 Molding material (weight %) Slurry Dough (1) (2) (3) (7) (4) (5)(6) (8) Starch Potato starch 50 25 40 50 0 25 25 65 DerivativeCross-linked 0 20 0 0 60 25 0 0 starch phosphate Total of starch 50 4540 50 60 50 25 65 Extending Okara (bean curd 0 0 0 0 0 0 15 0 agentrefuse) Beer yeast 0 0 0 0 0 0 10 0 residues Total of extending agents 00 0 0 0 0 25 0 (extending additives) Total main solids 50 45 40 50 50 5050 65 Strength Virgin pulp 0 0 5 0 0 10 0 0 adjusting Waste paper pulp 00 0 0 0 0 5 0 agent Calcium 0 0 0 0 10 5 0 0 carbonate PlasticizerSorbitor 0 1 0 0 2 0 2 2 Emulsifier Glycerin fatty 0 0.5 0 0 0 0 0 0acid ester Stabilizer Guar gum 0 2 0.5 0 0 0 0 0 Releasing Magnesium 00.5 0.5 0 1 1 1 0 agent stearate Expanding Sodium 0 0 0.5 4 2 2 0 0agent hydrocarbonate Coloring Cochineal 0 0 0.5 0 0 0 0 0 agent Total offunctional additives 0 4 7 4 7 18 8 2 Water 50 51 53 46 25 32 42 33

(Coating Film)

The five coating films F1, F2, F3, F4 and F5 shown in Table 2 wereprepared as the coating film.

TABLE 2 Thickness Softening Melting No. Type (m) point (° C.) point (°C.) F1 Polylactide {circle around (1)} 25 70 130 F2 Polylactide {circlearound (2)} 50 90 140 F3 Denatured Polyester {circle around (1)} 35 110150 F4 Denatured Polyester {circle around (2)} 50 130 170 F5 DenaturedPolyester {circle around (3)} 50 150 200

The coating films F3 to F5 made of denatured polyesters shown in Table2, have repeating units consisting of terephtharic acid, sulfonic metalsalt (sodium salt 5-sulfonic sulfate), aliphatic dicarboxylic acid(glutaric acid), ethylene glycol, and diethylene glycol, and these arearomatic polyester extended films that are biaxially stretched films ofaromatic polyester copolymer containing about 50 to 90 mole % ofterephtharic acid, about 0.2 to 6 mole % of sulfonic metal salt, andabout 4 to 49.8 mole % of aliphatic dicarboxylic acid of acidiccomponents, and about 50 to 99.9 mol % of ethylene glycol and about 0.1to 50 mole % of diethylene glycol of glycolic components.

Example 1

For all of the combinations (16 combinations in total) of 8 moldingmaterials (1) to (8) shown in Table 1 as the molding material 14 and twocoating films F3 and F5 shown in Table 2 as the coating film 12, a roundplate-shaped container 10 b was manufactured by the method of Embodiment1 explained with FIGS. 6 (a) and 6 (b).

Using the metal mold 20 b having the exhaust holes 31 b and 32 b shownin FIGS. 6 (a) and 6 (b) and with the cavity 25 b in uniform thicknessof 2.5 mm (corresponding to thickness of the round plate-shapedcontainer 10 b), the molding material 14 is placed between a pair ofcoating films 12 in the metal mold 20 b. Then, the metal mold is clampedby fitting the convex mold part 21 b in the concave mold part 22 b, themain body 11 b is obtained by heating and molding the molding material14 and the coating film 12 in the metal mold 20 b and steam-expandingthe molding material 14, and at the same time, the coating film 12 issoftened and pressure-bonded to the surface of the main body 11 b. Inaddition, air existing between the coating film 14 and the surface ofthe metal mold 20 b is discharged out of the metal mold 20 b through theexhaust holes 31 b and 32 b by internal pressure of the metal mold 20 bat the time of heating and molding.

As the heating method, external heating to heat the metal mold 20 b byan electric heater, and internal heating by high-frequency dielectricheating were used. Also, in case of using the coating film F3, thetemperature of the metal mold 20 b at the time of heating and moldingwas set at 130° C. In case of using the coating film F5, the temperatureof the metal mold 20 b was set at 160° C. at the time of heating andmolding.

Comparative Example 1

For comparison, a round plate-shaped container was manufactured asEmbodiment 1, except that a metal mold without the exhaust holes 31 band 32 b in the metal mold 20 b, that is, the metal mold that enclosesthe inside at the time of heating and molding is used instead of themetal mold 20 b.

Moldability of the round plate-shaped container was compared inreference with Example 1 using the metal mold 20 a with the exhaustholes 31 b and 32 b and Comparative Example 1 using the metal moldwithout the exhaust holes 31 b and 32 b. More particularly, theround-plate shaped container 10 b obtained by Example 1 and theround-plate shaped container for comparison obtained by ComparativeExample 1 were checked for (1) asperity on the flat area (bottom 10 baor flange 10 bc), (2) sharpness of an edge at the flange corner (cornerof a boundary between the flange 10 bc and the curved area 10 ba), (3)Thickness A of the center of the bottom 10 ba, thickness B of the flange10 bc and thickness C of the flange corner (sectional thickness).

The results below were obtained irrespective of type of the moldingmaterial 14 and the coating film 12.

As for (1), small concavities were found on the surface of the flat area(bottom or flange) of the round plate-shaped container in ComparisonExample 1. On the other hand, no concavity was found on the surface ofthe flat area (bottom 10 ba or flange 10 bc) of the round plate-shapedcontainer 10 b in Example 1.

As for (2), the round plate-shaped container of Comparative Example 1did not have a sharp edge at the flange corner, unlike a shape of thecavity. On the other hand, the round plate-shaped container 10 b ofExample 1 had a sharp edge at the flange corner because it was correctlymolded into the shape of the cavity 25 b.

As for (3), in the round plate-shaped container of Comparative Example1, there was some variation within 1 mm to 2.5 mm in a thickness of eachpart. Especially Thickness C of the flange corner was thin. On the otherhand, the round plate-shaped container 10 b of Example 1 was molded withhigher accuracy with a thickness within 2.3 mm to 2.5 mm.

From the above results, in the manufacturing method of the roundplate-shaped container 10 b, it was proven that moldability of thesurface at the flat area and the flange corner of the round plate-shapedcontainer 10 b by molding with the metal mold 20 b equipped with theexhaust holes 31 and 32 b.

Example 2

As for all of the combinations (16 combinations) of 8 molding materials(1) to (8) shown in Table 1 as the molding material 14 and two coatingfilms F3 and F5 shown in Table 2 as the coating film 12, the bowl-shapedcontainer 10 a of a deep drawing shape was manufactured by the method ofEmbodiment 1 explained with FIG. 1.

That is to say, using the metal mold 20 a with the exhaust holes 31 aand 32 a shown in FIGS. 5( a) and 5 (b) and having the cavity 25 a of auniform thickness of 2.5 mm (corresponding to the thickness of thebowl-shaped container 10 a), the molding material 14 was placed betweena pair of coating films 12 in the metal mold 20 a. Then, the metal mold20 a was clamped by fitting the convex mold part 21 a in the concavemold part 22 a, and the main body 11 a was obtained by heating andmolding the molding material 14 and the coating film 12 in the metalmold 20 a and steam-expanding the molding material. At the same time,the coating film 12 was softened and pressure-bonded to the surface ofthe main body 11 a. Then, at the time of heating and molding, airexisting between the coating film 14 and the surface of the metal mold20 a was discharged out of the metal mold 20 a through the exhaust holes31 a and 32 a by internal pressure of the metal mold 20 a.

As a heating method, external heating to heat the metal mold 20 a by anelectric heater and internal heating by high-frequency dielectricheating were both used. In case of using the coating film F3, thetemperature of the metal mold 20 a at the time of heating and moldingwas set at 130° C., and in case of using the coating film F5, thetemperature of the metal mold 20 a at the time of heating and moldingwas set at 160° C.

Comparative Example 2

The bowl-shaped container for comparison was manufactured as Example 2,except that a metal mold without the exhaust holes 31 a and 32 a in themetal mold 20 a, that is, the metal mold that encloses the inside at thetime of heating and molding was used instead of the metal mold 20 a.

Moldability of the bowl-shaped container was compared for Example 2using the metal mold 20 a with the exhaust holes 31 a and 32 a andComparative Example 2 using the metal mold without the exhaust holes 31a and 32 a. More particularly, the bowl-shaped container 10 a obtainedby Example 2 and the bowl-shaped container for comparison obtained byComparative Example 2 were checked for (1) asperity on the flat area(side wall 10 aa, flange 10 ac, the center (concave part) 10 ae of thebottom 10 ab), (2) shape of the flange corner (corner of the boundarybetween the flange 10 ac and the side wall 10 aa) and the foot 10 ad and(3) Thickness A of the center of the bottom 10 ab (thickness of theconcave part 10 ae), Thickness B of the foot 10 ad, thickness C of anouter periphery (concave part 10 af) of the foot 10 ad, Thickness D ofthe side wall 10 aa, and Thickness E of the flange corner (sectionalthickness).

The results below were obtained irrespective of the kind of moldingmaterial 14 and the coating film 12.

As for (1), small concavities were found on the surface of the flat area(side wall or flange) of the bowl-shaped container in Comparison Example2. On the other hand, no concavity was found on the surface of the flatarea (side wall 10 aa, flange 10 ac, the center (concave part) 10 ae ofthe bottom 10 ab) of the bowl-shaped container 10 a in Example 2.

As for (2), in the bowl-shaped container of Comparative Example 2, therewas a difference between the edge (corner) at the foot and flange cornerand those of the cavity in the shape and thickness. On the other hand,in the bowl-shaped container 10 a of Example 2, the foot 10 ad and theflange corner (corner of the flange 10 ac) is correctly molded into thesame shape as that of the cavity 25 b and has a sharp edge at theflange.

As for (3), in the bowl-shaped container of Comparative Example 2, therewas some variation within 0.5 mm to 2.5 mm in a thickness of each part,especially Thickness B of the foot 10 ad, Thickness C of the outerperiphery of the foot 10 ad and Thickness E of the flange corner werethin. On the other hand, the bowl-shaped container 10 a of Example 2 wasmolded with higher accuracy with a thickness of within 2.3 mm and 2.5 mmat each part.

From the above results, in the manufacturing method of the bowl-shapedcontainer 10 a of a deep drawing shape, it was proven that moldabilityis significantly improved by molding with the metal mold 20 a equippedwith the exhaust holes 31 a and 32 a compared with the case of the roundplate-shaped container 10 b.

Example 3

In this example, as shown in FIG. 18, the metal mold 20 a was used,which has almost the same structure as the metal mold 20 a shown inFIGS. 5( a) and 5(b).

The metal mold 20 a shown in FIG. 18 has the position of the exhaustholes 31 a and 32 a, shape and size of the cavity common to the metalmold 20 a shown in FIGS. 5( a) and 5(b). However, the space leading tothe cavity through the exhaust holes 31 a and 32 a (exhaust tube 33 a)formed inside the convex mold part 21 a (upper mold) and the concavemold part 22 a (lower mold) or the exhaust opening 34 are different fromthose of the metal mold 20 a shown in FIGS. 5 (a) and 5 (b).

That is to say, the exhaust opening 34 a was provided at an upper side(a side above the upper end of the cavity) of the convex mold part 21 a(upper mold), and one cylindrical exhaust tube 33 a (exhaust tube 33a-1) was provided horizontally toward a central axis of the convex mold21 a (vertical central axis) from the exhaust opening 34 a to a positionnear the central axis (position of an exhaust tube 33 a-6 mentionedbelow). Five vertical and cylindrically exhaust tubes 33 a linked withthe exhaust tube 33 a-1 and extending downward were provided (from theoutside the exhaust tubes 33 a-2, 33 a-3, 33 a-4, 33 a-5, and 33 a-6)and the end of these exhaust tubes 33 a-2 to 33 a-6 was positioned about5 mm apart from the molding surface (surface forming a cavity). Then, atthe end of the exhaust tubes 33 a-2 to 33 a-6 the exhaust hole 31 a waspierced through the molding surface. This structure (exhaust opening 34a, exhaust tubes 33 a-1 to 33 a-6 and the exhaust hole 31 a) wereprovided in four sets horizontally displaced at 90° to be symmetricalwith respect to the central axis.

The exhaust opening 34 a was provided on a side of the lower end of theconcave mold part 22 a (lower mold) and one cylindrical exhaust tube 33a (exhaust tube 33 a-1) was horizontally provided toward the centralaxis of the concave mold part 22 a from the exhaust opening 34 a to aposition near the central axis (position of the exhaust tube 33 a-6mentioned below). Three vertical and cylindrical exhaust tubes 33 alinked with the exhaust tube 33 a-1 and extending upward were provided(from the outside, the exhaust tubes 33 a-2, 33 a-3 and 33 a-4) and theend of these exhaust tubes 33 a-2 to 33 a-4 were positioned about 5 mmapart from the molding surface (surface forming the cavity). Then, theexhaust hole 32 a was pierced at the end of the exhaust tubes 33 a-2 to33 a-4 through the molding surface. This structure (exhaust opening 34a, exhaust tubes 33 a-1 to 33 a-4 and the exhaust hole 32 a) displacedat 90° on a horizontal line were provided in four sets to be symmetricalwith respect to the central axis of the concave mold part 22 a.

Then, the bowl-shaped container was manufactured as Example 2, exceptthat the metal mold 20 a shown in FIG. 18 was used instead of the metalmold 20 a shown in FIGS. 5( a) and 5 (b), and that the diameter of allthe exhaust tubes 33 a was 10 mm or 15 mm, the sectional shape of theexhaust holes 31 a and 32 a is round, ad the diameter of the exhaustholes 31 a and 32 a was changed to 0.3 mm, 0.4 mm, 0.5 mm, 0.7 mm, 1.0mm, 1.2 mm, 1.5 mm and 1.7 mm. The resulting bowl-shaped container wasevaluated for a thickness and surface condition.

The results below were obtained whether the diameter of the exhaust tube33 a is 10 mm or 15 mm. That is to say, in case that the diameter of theexhaust holes 31 a and 32 a is 0.3 mm (sectional area of the exhaustholes 31 a and 32 a is 0.07069 mm²), air confined between the moldingsurface in the cavity and the coating film 12 was not dischargedcompletely and desirable thickness was not obtained partially. On theother hand, in case that the diameter of the exhaust holes 31 a and 32 ais 1.5 mm (sectional area of the exhaust holes 31 a and 32 a is 1.767mm²), at the parts corresponding to the exhaust holes 31 a and 32 a inthe resultant bowl-shaped container, some protrusion was clearly foundon the coating film 12, and the bowl-shaped container having a smoothsurface was not obtained. In addition, in case that the diameter of theexhaust holes 31 a and 32 a is 1.7 mm (sectional area of the exhaustholes 31 a and 32 a is 2.270 mm²), at the parts corresponding to theexhaust holes 31 a and 32 a of the resultant bowl-shaped container, thecoating film 12 was partially torn.

On the other hand, in case that the diameter of the exhaust holes 31 aand 32 a is 0.4 to 1.2 mm (sectional area of the exhaust holes 31 a and32 a is 0.1257 to 1.131 mm²), there was no protrusion or tear on thecoating film 12 a and the excellent bowl-shaped container having a giventhickness was obtained. Table 3 shows these results.

TABLE 3 Diameter of 0.3 mm 0.4 to 1.5 mm 1.7 mm exhaust 1.2 mm holeSectional 0.07069 mm² 0.1257 to 1.767 mm² 2.270 mm² area of 1.131 mm²exhaust hole Evaluation Incomplete Good Clear Partially air exhaustProtrusion torn on the of the film film

From the results in Table 3, it has proven that in case that the exhaustholes 31 a and 32 a have a round section, the diameter of the exhaustholes 31 a and 32 a is preferably between 0.4 mm and 1.2 mm. However,the diameter is preferable only for the case that the exhaust holes 31 aand 32 a have a round section. In case that the exhaust holes 31 a and32 a have another sectional shape, they may be designed to obtain equalpressure loss depending on the shape. More particularly, since pressureloss is almost inversely related to the sectional area of the exhaustholes 31 a and 32 a, the exhaust holes 31 a and 32 a may be designed sothat the sectional area thereof may be equal to that of the exhaustholes 31 a and 32 a having a round sectional shape and 0.4 to 1.2 mm indiameter, that is 0.12 to 1.13 mm², regardless of the sectional shape ofthe exhaust holes 31 a and 32 a.

Example 4

The bowl-shaped container was manufactured as Example 3, except that thediameter of the exhaust holes 31 a and 32 a (round section) is fixed to0.7 mm and the diameter of all the exhaust tubes (cylindrical shape) ischanged to 3 mm, 5 mm, 10 mm 15 mm, and 20 mm.

For internal heating by high-frequency dielectric heating,high-frequency power supply (maximum output of 3 kW) was connected tothe convex mold part 21 a and the concave mold part 22 a and anodecurrent of the high-frequency power supply was set at 0.3 A. The moldingtime (heating time) was set at 110 seconds.

The resultant bowl-shaped container was evaluated for a thickness andsurface condition.

In result, in case that the diameter of the exhaust tube 33 a is 3 mm,air confined between the molding surface and the coating film 12 in thecavity was not discharged completely and a given thickness was notpartially obtained.

On the other hand, incase that the diameter of the exhaust tube 33 a is5 to 20 mm, there was no protrusion or tear on the coating film andexcellent bowl-shaped container having a given thickness was obtained.Table 4 shows these results.

TABLE 4 Diameter of exhaust 3 mm 5 to 20 mm tube Evaluation (0.3 A)Incomplete air Good exhaust

Also, a pressure sensor 40 was installed at the side of the moldingsurface of the concave mold part 22 a (lower mold) and connected to apressure gauge to measure a periodic change of internal pressure of thecavity during molding. The graph in FIG. 19 shows the change of internalpressure of the cavity during molding measured by the pressure gaugeconnected to the pressure sensor 40.

Example 5

The bowl-shaped container was manufactured as Example 4, except thatanode current of the high-frequency power supply (maximum output of 3kW) connected for internal heating is changed from 0.3 A to 1.0 A andmolding time (heating time) is reduced from 110 seconds to 60 seconds.

The resultant bowl-shaped container was evaluated for a thickness andsurface condition.

In result, this Example of 1.0 A of anode current and 60 seconds ofmolding time showed a different result from Example 4 of a lower anodecurrent of 0.3 A and longer molding time for 110 seconds. That is tosay, in case that the diameter of exhaust tube was 10 to 20 mm, internalpressure of the cavity was discharged at once and the expanded moldedarticle came through the coating film 12 and put in the exhaust holes 31a and 32 a. On the contrary, in case that the diameter of the exhausttube 33 a was 3 mm or 5 mm, a good result was obtained since internalpressure of the cavity was completely discharged, without causing anytear on the coating film. Table 5 shows these results.

TABLE 5 Diameter of 3 mm 5 mm 10 to 20 mm exhaust tube Evaluation GoodGood Tear (molding (1.0 A) material pierced through the film)

Also, as Example 4, a change of internal pressure of the cavity duringmolding (hereinafter sometimes referred to as “internal pressure) wasmeasured by the pressure gauge connected to the pressure sensor 40. FIG.19 shows the result. As a reference, FIG. 19 also shows the data incaseof applying external heating only without internal heating by highfrequency.

The reason of different results between Example 4 and Example 5 ispresumed below.

That is to say, as seen in FIG. 19, in steam expansion molding of thepresent invention, internal pressure rapidly increases together withevaporation and swelling of moisture in the molding material, and as atransition to a drying stage after completion of expanding stage, andwith progress of evaporation, internal pressure gradually decreases. Ifrelatively large energy is used for internal heating, initial speed ofinternal pressure increase rises, and maximum internal pressureincreases. (This phenomenon is characteristic of steam expansion moldingof the present invention, and it is much different from typical vacuummolding or pressurized molding wherein internal pressure of the cavityis consistent.

Thus, it is presumed that in case that relatively low high-frequencyenergy by 0.3 A of anode (when the same high-frequency oscillator(high-frequency power supply) is used, high-frequency energy caused bythe high-frequency oscillator is proportional to anode current of avacuum tube in the high-frequency oscillator) is only applied to themolding material, due to a small diameter of 3 mm of the exhaust tube,excessive air in the cavity was not discharged completely since pressureloss in the exhaust tube is relatively large and internal pressure isinsufficient, compared with pressure loss.

However, when the anode current is increased to 1.0 A, as shown in FIG.19, it is presumed that by a rapid increase of internal pressure and anincrease of maximum internal pressure, internal pressure exceedsrelatively large pressure loss in the exhaust tube 33 a of 3 mm indiameter and air is discharged. On the contrary, in case that thediameter of the exhaust tube 33 a is large (not less than 10 mm), adifference in pressure between the outside (side of the exhaust holes 31a and 32 a) and the inside (side of expanded molded article) sandwichingthe coating film 12 increases at one time when air is discharged at onceat a rapid increase of internal pressure, and expanded molded articlepierces through the coating film 12 at the exhaust holes 31 a and 32 a.

Example 6

As explained in Example 5, in case of a rapid increase of internalpressure in the cavity, a smaller diameter of exhaust holes 31 a and 32a obtained the better result. Next, another structure was evaluated thatan enclosed space is formed in the exhaust tube 33 a and air dischargedfrom the cavity by an increase of internal pressure of the cavityincreases pressure in the exhaust tube 33 a.

More particularly, the bowl-shaped container was manufactured as Example5, except that the exhaust opening 34 a is closed to make a space in theexhaust tube 33 a enclosed from the outside of the metal mold 20 a, andvolume of the enclosed space is changed for Void Capacity V in thecavity before heating and molding, as shown in Table 6. V is calculatedunder the following formula:V=(total capacity in the cavity)−(volume of the molding material)

-   -   The resultant bowl-shaped container was evaluated for a        thickness and surface condition. The results are shown in Table        6 irrespective of the diameter of the exhaust tube 33 a.

TABLE 6 Volume of enclosed space (⅕) V (⅓) V (½) V V 2 V 4 V EvaluationIncomplete Almost good Good Tear air exhaust

In result, it has proven that proper exhaust is possible by adjustingthe volume of the enclosed space in the exhaust tube 33 a irrespectiveof the diameter of the exhaust tube 33 a. That is to say, when thevolume of the enclosed space in the exhaust tube 33 a is formed to beequivalent to a third to twice of the Void Capacity V in the cavitybefore molding, there is no inconsistent thickness of the container dueto insufficient air exhaust, no tear on the coating film due toexcessive air exhaust, leading to good results. It is presumed that airexisting in the enclosed space inside the exhaust tube 33 a functions asa buffering material (air cushion) to reduce a stress applied to thecoating film 12 by the expanded molded article and any tears on thecoating film 12 caused by excessive air exhaust can be prevented.

Therefore, the method to form the enclosed space, so calledair-cushioning method, is especially effective in case of a rapidmolding as this Example or in case of weak strength of the coating film12.

Example 7

The bowl-shaped container 10 a was manufactured by a method of Example 2explained with FIG. 20, for all of the compositions (40 combinations intotal) of eight molding materials (1) to (8) shown in Table 1 and fivecoating films F1 to F5.

As a heating method, external heating to heat the metal mold 20 a by anelectric heater and internal heating by high-frequency dielectricheating were both used.

In this Example, all of these 40 combinations were manufactured undertwelve heating conditions with the metal mold 20 a set at thetemperature of 90° C., 100° C., 110° C., 120° C., 130° C., 140° C., 150°C., 160° C., 170° C., 180° C., 190° C., and 200° C.

The resultant 480 varieties of bowl-shaped container 10 a (samples) wereevaluated for expanded moldability, condition of the coating film aftermolding, and water resistance. As for expanded moldability, fineness andconsistency of the expanded texture of the main body 11 a were checked.In addition, the coating film after molding was checked for pinholes bydipping a normal sample in colored water containing a surface-activeagent after visually checking for abnormal tears.

The results below were obtained irrespective of the variety of themolding material and the coating film. That is to say, in case that thetemperature of the metal mold 20 a is less than the softening point ofthe coating film, the coating film was torn. In case that thetemperature of the metal mold 20 a is substantially equal to the meltingpoint of the coating film, the coating film had many pinholes. In casethat the temperature of the metal mold 20 a exceeds the melting point ofthe coating film, the coating film melted. In the other cases, thecoating film was in good condition without melting, tears, cracks orpinholes.

From the results above, it has proven that it is preferable thetemperature of the metal mold 20 a is not less than the softening pointof the coating film and at least 10° C. lower than the melting pointthereof.

On the other hand, the main body 11 a had better fineness andconsistency of the expanded texture, in case that the temperature of themetal mold 20 a is not less than 130° C., and it had much betterfineness and consistency in case that the temperature of the metal mold20 a is not less than 150° C.

Therefore, from these results; in cases that either one of the coatingfilms F2 to F5 is used as the coating film, the temperature of the metalmold 20 a is not less than the softening point of the coating film 12and at least 10° C. lower than the melting point thereof and not lessthan 130° C., both coating film and main body 11 a obtained goodresults.

Also, among these cases, if the coating film F4 or F5 is used as thecoating film, the temperature of the metal mold 20 a is not less thanthe softening point of the coating film 12 and at least 10° C. lowerthan the melting point thereof and not less than 130° C., the main bodyobtained better result.

Therefore, as for the softening point of the coating film a good resultwas obtained at not less than 90° C. and a better result was obtained atnot less than 130° C. Also, as for the melting point of the coatingfilm, a good result was obtained at not less than 140° C. and a betterresult was obtained at not less than 170° C.

Example 8

For all of the compositions (total 16 combinations) of eight moldingmaterials (1) to (8) shown in Table 1 and five coating films F3 and F5shown in Table 2, the bowl-shaped container 10 a was manufactured by thesame method as Embodiment 2 explained with FIG. 20

As a heating method, external heating to heat the metal mold 20 a by anelectric heater and internal heating by high-frequency dielectricheating were both used. In case of using the coating film F3, thetemperature of the metal mold 20 a was set at 130° C. at the time ofheating and molding, and in case of using the coating film F5, thetemperature of the metal mold 20 a was set at 160° C. at the time ofheating and molding.

Also, when both convex mold part 21 a and concave mold part 22 a weremoved to approximate each other, until the convex mold part 21 a and theconcave mold part 22 a contacted the coating film (until the coatingfilm 12 started to deform), both convex mold part 21 a and concave moldpart 22 a were moved to approximate each other. Afterwards, the convexmold part 21 a only was moved. Then, for all of these 16 compositions,moving speed of the convex mold part 21 a when it was only moved, waschanged between 5 mm/s and 20 mm/s at constant.

The resultant bowl-shaped container 10 a (sample) was evaluated forexpanded moldability, condition of the coating film after molding andwater resistance, as Example 7.

The results below were obtained irrespective of type of the moldingmaterials or coating films. That is to say, if the moving speed of theconvex mold part 21 a is between 8 mm/s and 12 mm/s, a very goodbowl-shaped container 10 a was obtained without tears, cracks orpinholes on the coating film. If the moving speed of the convex moldpart 21 a is slower than 8 mm/s, the coating film had more pinholes. Onthe contrary, if the moving speed of the convex mold part 21 a is fasterthan 12 mm/s, the coating film had more tears (tears or cracks).

Example 9

For all of the compositions (total 16 combinations) of eight moldingmaterials (1) to (8) shown in Table 1 and five coating films F3 and F5shown in Table 2, the cup-shaped container 10 c shown in FIG. 4 wasmanufactured by the same method as Embodiment 2 explained with FIG. 20

As a heating method, external heating to heat the metal mold 20 d by anelectric heater and internal heating by high-frequency dielectricheating were both used. In case of using the coating film F3, thetemperature of the metal mold 20 d was set at 130° C. at the time ofheating and molding, and in case of using the coating film F5, thetemperature of the metal mold 20 d was set at 160° C. at the time ofheating and molding.

As the metal mold 20 d, four metal molds 20 c having different surfacewere prepared: (1) metal mold 20 d of which vegetable oil was applied ona surface contacting on the coating film as a slip agent; (2) metal mold20 d of which magnesium stearate was applied on a surface contacting onthe coating film as a slip agent; (3) metal mold 20 d of whichtetrafluoroethylene plastic coating is formed on a surface contacting onthe coating film as a slip agent; (4) metal mold 20 d of which no slipagent is applied on a surface contacting on the coating film. For all 16combinations of raw materials, the cup-shaped container 10 b wasmanufactured using four metal molds 20 d.

The resultant cup-shaped container 10 c (sample) was evaluated forexpanded moldability, condition of the coating film after molding andwater resistance, as Example 7.

The results below were obtained irrespective of type of the moldingmaterials and the coating films.

That is to say, in case of (4) using the metal mold 20 d without a slipagent on the surface contacting on the coating film, the coating filmhad tears or pinholes. Especially, in case of (4) using the coating filmF5, the coating film had more tears or pinholes.

On the other hand, in case of (1) to (3) using the metal mold 20 d witha slip agent on the surface contacting on the coating film, the coatingfilm had no tears or pinholes. Also, in these cases of (1) to (3),expanded moldability was good and the slip agent gave no bad effect. Forthe case (3) using tetrafluoroethylene plastic coating, the surface ofthe coating film was the most beautiful with no adhesion of the slipagent.

As mentioned above, the method to manufacture a biodegradable moldedarticle of the present invention is a method to use a slurry or doughmolding material mainly made of starch or a derivative thereof andobtained by mixing water therewith, and a coating film mainly made of abiodegradable plastic and having hydrophobicity, mold the moldingmaterial through steam expansion by heating and molding the moldingmaterial and the coating film in a mold having a specific shape ofcavity, and at the same time soften and pressure-bond the coating filmon a surface of the biodegradable expanded molded article obtainedthrough steam expansion molding, wherein an exhaust hole is provided inthe mold to discharge air existing between the coating film and thesurface of the mold through the exhaust hole out of the cavity at thetime of heating and molding.

According to the method above, it is possible to exert more excellentstrength compared with a conventional molded article made of starchsince the resultant biodegradable expanded molded article containsmoderate moisture. Also, according to the method above, since thecoating film having hydrophobicity is pressure-bonded on the surface ofthe biodegradable expanded molded article through heating and molding inthe mold, it is possible to obtain the biodegradable molded articlewhere the coating film is substantially adhered to the surface, and tomanufacture the biodegradable molded article having enough waterresistance. Moreover, according to the above method, the biodegradableexpanded molded article is an expanded object having a large surfacearea, resulting in a very excellent biodegradability. According to themethod above, since steam expansion molding of the molding material andpressure-bonding of the coating film is performed at one time, thebiodegradable molded article can be manufactured with less processes.

Therefore, the above method has an advantage that a biodegradable moldedarticle having a complicated shape can be easily manufactured withenough strength, enough water resistance and very excellentbiodegradability.

Furthermore, according to the method above, since gaseous matterexisting between the coating film and the surface of the mold isdischarged out of the cavity through the exhaust hole at the time ofheating and molding, adhesiveness of the coating film to the surface ofthe mold is improved. Accordingly, in the method above, it is possibleto obtain the biodegradable molded article having excellent surfacesmoothness and to mold the biodegradable molded article with goodaccuracy of dimension.

In addition, the mold of the present invention, as mentioned above, is amold to heat a slurry or dough molding material inside mainly made ofstarch or a derivative thereof and obtained by adding water thereto andmold through steam expansion, consisting of a plurality of mold partsthat can fit together and form a specific shape of cavity inside, andhaving an exhaust hole piercing through each of the mold parts todischarge gaseous matter in the cavity outside.

According to the structure above, when the molding material is moldedthrough steam expansion by heating the molding material inside, gaseousmatter in the cavity can be discharged out of the cavity through theexhaust hole. This can improve adhesiveness of the molded article to thesurface of the mold. Accordingly, the above structure has an advantageto provide a mold that can mold the biodegradable molded article havingexcellent surface smoothness with good accuracy of dimension.

Also, the method to manufacture a biodegradable molded article of thepresent invention is a method to manufacture a biodegradable moldedarticle of a deep drawing shape by placing a molding material and acoating film substantially flat in a mold of a deep drawing shape toheat and mold them.

According to the method above, a biodegradable molded article having acomplicated shape can be easily manufactured with enough strength,enough water resistance and very excellent biodegradability. Inaddition, according to the method above, it is possible to manufacture abiodegradable molded article of a deep drawing shape such as abowl-shaped container or a cup-shaped container with fewer processes.

Moreover, the method to manufacture a biodegradable molded article ofthe present invention is, as mentioned above, a method to use a moldconsisting of a pair of convex mold and concave mold, place a moldingmaterial and a coating film between the convex mold and the concavemold, deform the center of the coating film by moving at least eitherone of the convex mold and the concave mold in the direction to fit ineach other at the time of heating and molding, and maintain a relativemoving speed of the convex mold to a surface formed by connecting asurface of a non-deforming part on an outer periphery of the coatingfilm within 8 mm/s to 12 mm/s, at least while the coating film is beingdeformed.

The method to manufacture a biodegradable molded article of the presentinvention, as mentioned above, is a method to do heating so that atemperature of the mold is not less that the softening point of thecoating film and 10° C. lower than the melting point thereof.

According to each of the methods above, especially in case that abiodegradable molded article of a deep drawing shape is manufacturedusing a substantially flat coating film, it is possible to preventdefects in the coating film more certainly and to secure waterresistance of the biodegradable molded article more steadily.

The embodiments or examples shown in “BEST MODE FOR CARRYING OUT THEINVENTION” are intended to disclose technical information on the presentinvention, and it should not be interpreted that the present inventionis limited to these examples or embodiments in narrow sense. The presentinvention can be executed by making various changes within the range ofthe claims described below and under the spirit of the presentinvention. The embodiments obtained by properly combining technicalmeasures disclosed in each embodiment is included within the technicalrange of the present invention.

INDUSTRIAL APPLICABILITY

The biodegradable molded article manufactured under the presentinvention can be desirably used for a molded article for packaging, suchas buffering materials, GES, packaging tray, and for a food containerincluding a container for ready-to-serve foods such as ready-to-serveChinese or Japanese noodles and baked noodles, a disposable plate ortray used for foodservice industry, and a container for soup or juice.

The biodegradable molded article of a shallow drawing shape manufacturedunder the present invention can be desirably used for a molded articlefor packaging, such as buffering materials, GES, packaging tray, and fora food container such as a one-way tray or plate used for thefoodservice industry.

Especially, the biodegradable molded article can be desirably used for acontainer for foods of higher moisture content due to its waterresistance, and can be desirably used also as a container forready-to-serve foods that can store ready-to-serve noodles for a certainperiod of time, due to its gas impermeability. Especially, thebiodegradable molded article manufactured under the present inventionhas high resistance of hot water, so it can be desirably used as acontainer for ready-to-serve foods including ready-to-server noodles inwhich hot water is poured.

As mentioned above, according to the method to use a mold with anexhaust hole of the present invention, it is possible to manufacture thebiodegradable molded article easily and with excellent accuracy ofdimension, having enough strength, enough water resistance, veryexcellent biodegradability and excellent surface smoothness, even thoughthe biodegradable molded article has a complicated shape.

As mentioned above, according to the method to place the moldingmaterial and the coating film substantially flat in the metal of a deepdrawing shape, it is possible to manufacture a biodegradable moldedarticle of a deep drawing shape with fewer processes, having enoughstrength, enough water resistance, and very excellent biodegradabilityeven though the biodegradable molded article has a complicated shape.

Also, as mentioned above, according to the method to maintain a relativemoving speed of a convex mold in accordance with the present inventionwithin a given range, or to meet specific conditions of a temperature ofthe metal mold in accordance with the present invention, it is possibleto easily manufacture a biodegradable molded article having enoughstrength, enough water resistance and very excellent biodegradabilityand no defects on the coating film, even though the biodegradable moldedarticle has a complicated shape.

Therefore, the mold and manufacturing method of the present inventioncan be desirably used to manufacture various biodegradable moldedarticles mentioned above.

1. A method to manufacture a biodegradable molded article comprising thesteps of: providing a slurry or dough molding material mainly made ofstarch or a derivative thereof and obtained by adding water therewith;providing a coating film distinct from the slurry or dough moldingmaterial and mainly made of a biodegradable plastic and havinghydrophobicity; placing the slurry or dough molding material and thecoating film into a mold having a given-shaped cavity to obtain acombination of the slurry or dough molding material and the coatingfilm; and heating and molding the combination of the slurry or doughmolding material and the coating film in the mold to mold the slurry ordough molding material through steam expansion, and at the same timesoften and pressure-bond the coating film to a surface of abiodegradable expanded molded article obtained through steam expansionmolding, wherein a mold made up of a pair of a convex mold and a concavemold being used; said mold has an exhaust hole; the molding material andthe coating film being placed between the convex mold and the concavemold before the heating and molding; in the heating and molding step, acentral part of the coating film being deformed by moving at leasteither one of the convex mold and the concave mold in a directionwherein these two molds fit together; at least while the coating film isbeing deformed, a relative moving speed of the convex mold to a planeformed by connecting a surface of non-deforming parts on an outerperiphery of the coating film being maintained from 8 mm/s to 12 mm/s;and in the heating and molding step, a gas existing between the coatingfilm and a surface of the mold is discharged out of the cavity throughthe exhaust hole.
 2. A method to manufacture the biodegradable moldedarticle as set forth in claim 1, wherein a space leading to the cavitythrough the exhaust hole is formed inside the mold, and in the heatingand molding step, the space is hermetically separated from outside themold.
 3. A method to manufacture the biodegradable molded article as setforth in claim 2, wherein the hermetically separated space has a volumeset between a third and twice that of a void in the cavity beforeheating and molding.
 4. A method to manufacture the biodegradable moldedarticle as set forth in claim 1, wherein the exhaust hole has a crosssection between 0.12 mm² and 1.13 mm².
 5. A method to manufacture abiodegradable molded article comprising the steps of: providing a slurryor dough molding material mainly made of starch or a derivative thereofand obtained by adding water thereto; providing a coating film distinctfrom the slurry or dough molding material and mainly made of abiodegradable plastic and having hydrophobicity; placing the slurry ordough molding material and the coating film into a mold having agiven-shaped cavity to obtain a combination of the slurry or doughmolding material and the coating film; and heating and molding thecombination of the slurry or dough molding material and the coating filmin the mold to mold the slurry or dough molding material through steamexpansion, and at the same time soften and pressure-bond the coatingfilm to a surface of a biodegradable expanded molded article obtainedthrough steam expansion molding, wherein the given-shaped cavity of themold has a deep drawing shape, and the mold is made up of a pair of aconvex mold and a concave mold; before the heating and molding, themolding material and the coating film being placed between the convexmold and the concave mold therein are substantially; in the heating andmolding step, a central part of the coating film being deformed bymoving at least either one of the convex mold and the concave mold in adirection wherein these two molds fit together, and at least while thecoating film is being deformed, a relative moving speed of the convexmold to a plane formed by connecting a surface of non-deforming parts onan outer periphery of the coating film being maintained from 8 mm/s to12 mm/s, so as to manufacture a biodegradable molded article of a deepdrawing shape.
 6. A method to manufacture the biodegradable moldedarticle as set forth in claim 1, wherein a mold made up of a pair of aconvex mold and a concave mold is used, the molding material and thecoating film are placed between the convex mold and the concave moldbefore the heating and molding, in the heating and molding step, acentral part of the coating film is deformed by moving at least eitherone of the convex mold and the concave mold in a direction where thesetwo molds fit together, and at least while the coating film is beingdeformed, the convex mold and the concave mold are straightly movedcloser to each other.
 7. A method to manufacture the biodegradablemolded article as set forth in claim 1, wherein a mold made up of a pairof a convex mold and a concave mold is used, the molding material andthe coating film are placed between the convex mold and the concave moldbefore the heating and molding, in the heating and molding step, acentral part of the coating film is deformed by moving at least eitherone of the convex mold and the concave mold in a direction where thesetwo molds fit together, and at least until the coating film starts todeform, both the convex mold and the concave mold are moved closer toeach other.
 8. A method to manufacture a biodegradable molded articlecomprising the steps of: preparing: a slurry or dough molding materialmainly made of starch or a derivative thereof and obtained by addingwater thereto; and a coating film mainly made of a biodegradable plasticand having hydrophobicity; and heating and molding the molding materialand the coating film in a mold having a given-shaped cavity to moldingan expanded molded article through steam expansion by, and at the sametime soften and pressure-bond the coating film to a surface of abiodegradable expanded molded article, a mold made up of a pair of aconvex mold and a concave mold being used, the molding material and thecoating film being placed between the convex mold and the concave moldbefore the heating and molding, in the heating and molding step, acentral part of the coating film being deformed by moving at leasteither one of the convex mold and the concave mold in a directionwherein these two molds fit together, and at least while the coatingfilm is being deformed, a relative moving speed of the convex mold to aplane formed by connecting a surface of non-deforming parts on an outerperiphery of the coating film being maintained from 8 mm/s to 12 mm/s.9. A method to manufacture the biodegradable molded article as set forthin claim 8, wherein the convex mold and the concave mold are straightlymoved closer to each other at least while the coating film is deformed.10. A method to manufacture the biodegradable molded article as setforth in claim 8, wherein both of the convex mold and the concave moldare moved to approximate each other at least until the coating filmstarts to deform.
 11. A method to manufacture the biodegradable moldedarticle as set forth in claim 1, wherein the heating is done so that themold has a temperature not less than a softening point of the coatingfilm and at least 10° C. lower than the melting point thereof.
 12. Amethod to manufacture a biodegradable molded article comprising thesteps of: providing a slurry or dough molding material mainly made ofstarch or a derivative thereof and obtained by adding water thereto;providing a coating film distinct from the slurry or dough moldingmaterial and mainly made of a biodegradable plastic and havinghydrophobicity; placing the slurry or dough molding material and thecoating film into a mold having a given-shaped cavity to obtain acombination of the slurry or dough molding material and the coatingfilm; and heating and molding the combination of the slurry or doughmolding material and the coating film in the mold to mold thebiodegradable expanded molded article through steam expansion, and atthe same time soften and pressure-bond the coating film to a surface ofa biodegradable expanded molded article, a mold made up of a pair of aconvex mold and a concave mold being used, the molding material and thecoating film being placed between the convex mold and the concave moldbefore the heating and molding, in the heating and molding step, acentral part of the coating film being deformed by moving at leasteither one of the convex mold and the concave mold in a directionwherein these two molds fit together, at least while the coating film isbeing deformed, a relative moving speed of the convex mold to a planeformed by connecting a surface of non-deforming parts on an outerperiphery of the coating film being maintained from 8 mm/s to 12 mm/s,and said heating being done so that the mold has a temperature not lessthan a softening point of the coating film and at least 10° C. lowerthan a melting point thereof.
 13. A method to manufacture thebiodegradable molded article as set forth in claim 11, wherein theheating is done so that the mold has a temperature not less than 130° C.14. A method to manufacture the biodegradable molded article as setforth in claim 11, wherein the heating is done so that the mold has atemperature not less than 150° C.
 15. A method to manufacture thebiodegradable molded article as set forth in claim 1, wherein a slipagent is applied to a surface of the mold contacting the coating filmbefore the heating and molding.
 16. A method to manufacture thebiodegradable molded article as set forth in claim 15, wherein the slipagent is a fluoroplastic layer formed on a surface of the mold.
 17. Amethod to manufacture the biodegradable molded article as set forth inclaim 1, wherein the coating film is a film mainly made of a denaturedpolyester.
 18. A method to manufacture the biodegradable molded articleas set forth in claim 1, wherein the coating film is a biaxiallystretched film.
 19. A method to manufacture the biodegradable moldedarticle as set forth in claim 2, wherein the exhaust hole has a crosssection between 0.12 mm² and 1.13 mm².
 20. A method to manufacture thebiodegradable molded article as set forth in claim 3, wherein theexhaust hole has a cross section between 0.12 mm² and 1.13 mm².
 21. Amethod to manufacture the biodegradable molded article as set forth inclaim 5, wherein a mold made up of a pair of a convex mold and a concavemold is used, the molding material and the coating film are placedbetween the convex mold and the concave mold before the heating andmolding, in the heating and molding step, a central part of the coatingfilm is deformed by moving at least either one of the convex mold andthe concave mold in a direction where these two molds fit together, andat least while the coating film is being deformed, the convex mold andthe concave mold are straightly moved closer to each other.
 22. A methodto manufacture the biodegradable molded article as set forth in claim 5,wherein a mold made up of a pair of a convex mold and a concave mold isused, the molding material and the coating film are placed between theconvex mold and the concave mold before the heating and molding, in theheating and molding step, a central part of the coating film is deformedby moving at least either one of the convex mold and the concave mold ina direction where these two molds fit together, and at least until thecoating film starts to deform, both the convex mold and the concave moldare moved closer to each other.
 23. A method to manufacture thebiodegradable molded article as set forth in claim 9, wherein both ofthe convex mold and the concave mold are moved to approximate each otherat least until the coating film starts to deform.
 24. A method tomanufacture the biodegradable molded article as set forth in claim 5,wherein the heating is done so that the mold has a temperature not lessthan a softening point of the coating film and at least 10° C. lowerthan the melting point thereof.
 25. A method to manufacture thebiodegradable molded article as set forth in claim 8, wherein theheating is done so that the mold has a temperature not less than asoftening point of the coating film and at least 10° C. lower than themelting point thereof.
 26. A method to manufacture the biodegradablemolded article as set forth in claim 12, wherein the heating is done sothat the mold has a temperature not less than 130° C.
 27. A method tomanufacture the biodegradable molded article as set forth in claim 12,wherein the heating is done so that the mold has a temperature not lessthan 150° C.
 28. A method to manufacture the biodegradable moldedarticle as set forth in claim 5, wherein a slip agent is applied to asurface of the mold contacting the coating film before the heating andmolding.
 29. A method to manufacture the biodegradable molded article asset forth in claim 8, wherein a slip agent is applied to a surface ofthe mold contacting the coating film before the heating and molding. 30.A method to manufacture the biodegradable molded article as set forth inclaim 5, wherein the coating film is a film mainly made of a denaturedpolyester.
 31. A method to manufacture the biodegradable molded articleas set forth in claim 8, wherein the coating film is a biaxiallystretched film.
 32. A method to manufacture the biodegradable moldedarticle as set forth in claim 8, wherein the coating film is a filmmainly made of a denatured polyester.
 33. A method to manufacture thebiodegradable molded article as set forth in claim 5, wherein thecoating film is a biaxially stretched film.